Fix AJ wrong deprecation message on `after_callbacks_if_terminated`:

- ### Problem

  In some cirumstances, the deprecation message to warn that AJ won't
  run `after_(enqueue/perform)` callbacks when the chain is halted
  by a `throw(:abort)` will be thrown even though no `throw(:abort)`
  was thrown.

  ```ruby
    run_callback(:foo) do
      ...
    end
  ```

  There is two possible way for the callback body to not be executed:

  1) `before` callback throw a `abort`
  2) `before` callback raises an error which is rescued by an
     around callback (See associated test in this commit for
     an example)

  When 2) happen we don't want to output a deprecation message,
  because what the message says isn't true and doesn't apply.

  ### Solution

  In order to differentiate between 1) and 2), I have added
  a `halted_callback_hook` which is called by ActiveSupport callback
  whenever the callback chain is halted.

- The `halted_callback_hook` method is called whenever the
  `terminator` halt the callback execution.
  Usually, this translate to when a `before` callback throw
  an `:abort`.

  <details>
    <summary> Example </summary>

    ```ruby
      class Foo
        include ActiveSupport::Callbacks

	define_callbacks :save
	set_callback(:save, :before) { throw(:abort) }

	def run
	  run_callbacks(:save) do
	    'hello'
	  end
	end

	def halted_callback_hook(filter)
	  # filter is the proc passed to `set_callback` above
	end
      end
    ```
  </details>

  ### Problem

  When a class has multiple callbacks, (i.e. `save`, `validate` ...),
  it's impossible to tell in the halted_callback_hook which type of
  callback halted the execution.
  This is useful to take different action based on the callback.

  <details>
    <summary> Use Case </summary>

    ```ruby
      class Foo
        include ActiveSupport::Callbacks

	define_callbacks :save
	define_callbacks :validate

	set_callback(:save, :before) { throw(:abort) }
	set_callback(:validate, :before) { throw(:abort) }

	def run
	  run_callbacks(:validate) do
	    ...
	  end

	  run_callbacks(:save) do
	    ...
	  end
	end

	def halted_callback_hook(filter)
	  Rails.logger.warn("Couldn't save the record, the ??? callback halted the execution")
	end
      end
    ```
  </details>

  ### Solution

  Allow `halted_callback_hook` to receive a second argument which is
  the name of the callback being run.

Simplify route score

Add activerecord/db/ to gitignore

After running `bundle exec rake test:sqlite3` and `bundle exec rake test:sqlite3_mem`
on my VM I noticed that it had created untracked files:

```bash
vagrant@ubuntu-bionic:/rails/activerecord$ git status
Untracked files:
  (use "git add <file>..." to include in what will be committed)
        db/
        file::memory:
```

To prevent them from being accidentally committed I put 'file::memory:' to
`activerecord/db/` folder and added the folder to .gitignore
Also, we could consider fixing this by removing `db/` folder in each test that
creates the folder.

It would be great if someone confirms that it happens not only on my VM.

Fixed typo classsic -> classic [ci skip]

Fix error in deprecation

[ci skip] Security guide: change raw HTML elements and signs to backquoted ones

When I implemented the deprecation for #38536 I left in the setter in
the initalizer. This meant that objects returned had both `@name` and
`@spec_name` set and objects looked like this:

```
<ActiveRecord::DatabaseConfigurations::HashConfig:0x00007fe0f7100c68
  @env_name="development",
  @name="primary",
  @spec_name="primary",
  @config={
    :adapter=>"mysql2",
    :database=>"recipes_app_development"
  }
>
```

Since we don't use the kwarg to create the hash config and we have the
reader for reading off the object or selecting from the configurations
objects list we can remove this so the object looks like:

```
<ActiveRecord::DatabaseConfigurations::HashConfig:0x00007fe0f7100c68
  @env_name="development",
  @name="primary",
  @config={
    :adapter=>"mysql2",
    :database=>"recipes_app_development"
  }
>
```

Testing Guides: Added section on Parallell Testing of Transactions

Based on https://github.com/rails/rails/issues/38578, it would be nice to have some information on transactions in test cases

Closes #37435.

ActionText is using ActionView in a way that ActionView doesn't have in
it's test suite.  This is just a regression test to hit that same use
case.

[ci skip] Documentation: Use yml extension for locale files example

The default extension we use for locale files is `.yml`. This patch
reflects this in the documentation example.

Dumps the schema or structure of a database when calling db:migrate:name

Fix `unscope` when an `eq` node which has no arel attribute

Resets the `ActiveRecord::Base` connection after `rails db:migrate:name`

Remove unused argument

Current code expect an `eq` node has one arel attribute at least, but an
`eq` node may have no arel attribute (e.g. `Arel.sql("...").eq(...)`).

In that case `unscope` will raise `NoMethodError`:

```
% bundle exec ruby -w -Itest test/cases/relations_test.rb -n test_unscope_with_arel_sql
Using sqlite3
Run options: -n test_unscope_with_arel_sql --seed 4477

# Running:

E

Error:
RelationTest#test_unscope_with_arel_sql:
NoMethodError: undefined method `name' for #<Arel::Nodes::Quoted:0x00007f9938e55960>
    /Users/kamipo/src/github.com/rails/rails/activerecord/lib/active_record/relation/where_clause.rb:157:in `block (2 levels) in except_predicates'
    /Users/kamipo/src/github.com/rails/rails/activerecord/lib/arel.rb:57:in `fetch_attribute'
    /Users/kamipo/src/github.com/rails/rails/activerecord/lib/active_record/relation/where_clause.rb:157:in `block in except_predicates'
    /Users/kamipo/src/github.com/rails/rails/activerecord/lib/active_record/relation/where_clause.rb:156:in `reject'
    /Users/kamipo/src/github.com/rails/rails/activerecord/lib/active_record/relation/where_clause.rb:156:in `except_predicates'
    /Users/kamipo/src/github.com/rails/rails/activerecord/lib/active_record/relation/where_clause.rb:31:in `except'
    /Users/kamipo/src/github.com/rails/rails/activerecord/lib/active_record/relation/query_methods.rb:487:in `block (2 levels) in unscope!'
    /Users/kamipo/src/github.com/rails/rails/activerecord/lib/active_record/relation/query_methods.rb:481:in `each'
    /Users/kamipo/src/github.com/rails/rails/activerecord/lib/active_record/relation/query_methods.rb:481:in `block in unscope!'
    /Users/kamipo/src/github.com/rails/rails/activerecord/lib/active_record/relation/query_methods.rb:471:in `each'
    /Users/kamipo/src/github.com/rails/rails/activerecord/lib/active_record/relation/query_methods.rb:471:in `unscope!'
    /Users/kamipo/src/github.com/rails/rails/activerecord/lib/active_record/relation/query_methods.rb:464:in `unscope'
    test/cases/relations_test.rb:2062:in `test_unscope_with_arel_sql'
```

We should check for both `value.left` and `value.right` those are arel
attribute or not.

This was leftover in debugging we did to support `shard` in
`connected_to`. We don't need this because `with_shard` already has
access to `connection_specification_name` because they are in the same
class.

Disallow calling `connected_to` on subclasses of `ActiveRecord::Base`

Behavior has not changed here but the previous API could be
misleading to people who thought it would switch connections for only
that class. `connected_to` switches the context from which we are
getting connections, not the connections themselves.
Co-authored-by: NJohn Crepezzi <john.crepezzi@gmail.com>

Simplify fixture resolver

Update some references to finder options [ci skip]

Use type attribute in ActionView::Helpers::JavaScriptHelper#javascript_tag example

https://gist.github.com/kamipo/296b9dd97f690d7960fdfe8de3ca08c7

Before:

```
================================= All symbols ==================================

Warming up --------------------------------------
   assign_attributes     4.425k i/100ms
Calculating -------------------------------------
   assign_attributes     44.983k (± 2.8%) i/s -    225.675k in   5.020906s

==================================== Mixed =====================================

Warming up --------------------------------------
   assign_attributes     4.546k i/100ms
Calculating -------------------------------------
   assign_attributes     46.103k (± 5.2%) i/s -    231.846k in   5.046489s

================================= All strings ==================================

Warming up --------------------------------------
   assign_attributes     4.511k i/100ms
Calculating -------------------------------------
   assign_attributes     47.931k (± 7.4%) i/s -    239.083k in   5.023971s
```

After:

```
================================= All symbols ==================================

Warming up --------------------------------------
   assign_attributes     4.831k i/100ms
Calculating -------------------------------------
   assign_attributes     48.206k (± 8.5%) i/s -    241.550k in   5.058372s

==================================== Mixed =====================================

Warming up --------------------------------------
   assign_attributes     4.960k i/100ms
Calculating -------------------------------------
   assign_attributes     50.628k (± 3.5%) i/s -    252.960k in   5.002779s

================================= All strings ==================================

Warming up --------------------------------------
   assign_attributes     5.006k i/100ms
Calculating -------------------------------------
   assign_attributes     52.242k (± 5.5%) i/s -    260.312k in   5.001695s
```

[ci skip]

Before:

```
DEPRECATION WARNING: spec_name is deprecated and will be removed from Rails 6.2 (spec_name accessors are deprecated and will be removed in Rails 6.2, please use name instead.)
```

After:

```
DEPRECATION WARNING: spec_name is deprecated and will be removed from Rails 6.2 (please use name instead)
```

Follow up of #38536.