Remove comment from `actiontext/actiontext.gemspec`

Fix API docs of `ActionText::RichText` [ci skip]

Use ES6 and Webpacker in ActionCable guide.

This comment was autogenerated, see
`railties/lib/rails/generators/rails/plugin/templates/%name%.gemspec.tt`
Since actiontext is well described in this file, I think we shouldn't
keep this comment. Note that this commit is more like cosmetic change,
so it is OK if we don't merge this.

This text should appear on the page
https://api.rubyonrails.org/v6.0/classes/ActionText/RichText.html

Related to 86517942

Import Action Text

Also, make tests and examples for individual execution counters
clearer, as it wasn't entierly clear what would happen in this case:

```
retry_on CustomException, OtherException, attempts: 3
```

The job would be retried at most 3 times in total, for both
CustomException and OtherException. To have the job retry 3 times at
most for each exception individually, the following retry_on
declarations are necessary:

```
retry_on CustomException, attempts: 3
retry_on OtherException, attempts: 3
```

[ci skip]

When using the `rich_text_area_tag` form helper from within a Rails
engine, the direct_upload_url and blob_url_template options would
default to non-existent routes.

By prefixing these routes with `main_app` we ensure the application
root is used rather than the engine.

Test Action Mailbox configurations

Fix `new_framework_defaults_6_0.rb` file

Add `ActiveModel::Errors#of_kind?`

Clarify `delegate_missing_to` [ci skip]

Since #34864 removed explicit receiver to clarify the
purpose of `delegate_missing_to`, I think it will be
better to do the same a few lines above to easier figure
out that `delegate_missing_to` defines `method_missing`,
`respond_to_missing?` when comparing these examples.

`Rails.application.config.active_job.return_false_on_aborted_enqueue`
should be commented as well.

Related to https://github.com/rails/rails/commit/0d40c62213cf0be58a470637bd364e92c5666402

Related to https://github.com/rails/rails/pull/34817#issuecomment-451508668

Match Action Mailbox, which sets a default queue for each of its two jobs.

Clarify benefit of `delegate_missing_to`

Removing the explicit receiver clarifies the purpose of `delegate_missing_to`.

Don't expect defined protect_against_forgery? in {token,csrf_meta}_tag

Fix example of I18n setting in the guide [ci skip]

Since #34356 logging `locale` value is more correct

For fixtures share the connection pool when there are multiple handlers

Make average compatible across ruby versions

Since Ruby 2.6.0 NilClass#to_d is returning `BigDecimal` 0.0, this
breaks `average` compatibility with prior Ruby versions. This patch
makes `average` return `nil` in all Ruby versions when there are no
rows.

This reverts commit 89b4612f.

Update the "Configuring Rails Applications" guide [ci skip]

Add section "Results of `load_defaults`" to the guide.

`nil`, `Numeric`, and `String` are most basic objects which are passed
to `type_cast`. But now each `when *types_which_need_no_typecasting`
evaluation allocates extra two arrays, it makes `type_cast` slower.

The `types_which_need_no_typecasting` was introduced at #15351, but the
method isn't useful (never used any adapters) since all adapters
(sqlite3, mysql2, postgresql, oracle-enhanced, sqlserver) still
overrides the `_type_cast`.

Just expanding the method would make the `type_cast` 2x faster.

```ruby
module ActiveRecord
  module TypeCastFast
    def type_cast_fast(value, column = nil)
      value = id_value_for_database(value) if value.is_a?(Base)

      if column
        value = type_cast_from_column(column, value)
      end

      _type_cast_fast(value)
    rescue TypeError
      to_type = column ? " to #{column.type}" : ""
      raise TypeError, "can't cast #{value.class}#{to_type}"
    end

    private
      def _type_cast_fast(value)
        case value
        when Symbol, ActiveSupport::Multibyte::Chars, Type::Binary::Data
          value.to_s
        when true       then unquoted_true
        when false      then unquoted_false
        # BigDecimals need to be put in a non-normalized form and quoted.
        when BigDecimal then value.to_s("F")
        when nil, Numeric, String then value
        when Type::Time::Value then quoted_time(value)
        when Date, Time then quoted_date(value)
        else raise TypeError
        end
      end
  end
end

conn = ActiveRecord::Base.connection
conn.extend ActiveRecord::TypeCastFast

Benchmark.ips do |x|
  x.report("type_cast") { conn.type_cast("foo") }
  x.report("type_cast_fast") { conn.type_cast_fast("foo") }
  x.compare!
end
```

```
Warming up --------------------------------------
           type_cast    58.733k i/100ms
      type_cast_fast   101.364k i/100ms
Calculating -------------------------------------
           type_cast    708.066k (± 5.9%) i/s -      3.583M in   5.080866s
      type_cast_fast      1.424M (± 2.3%) i/s -      7.197M in   5.055860s

Comparison:
      type_cast_fast:  1424240.0 i/s
           type_cast:   708066.0 i/s - 2.01x  slower
```

Add `--skip-action-mailbox` option to `rails new`

In an application that has a primary and replica database the data
inserted on the primary connection will not be able to be read by the
replica connection.

In a test like this:

```
test "creating a home and then reading it" do
  home = Home.create!(owner: "eileencodes")

  ActiveRecord::Base.connected_to(role: :default) do
    assert_equal 3, Home.count
  end

  ActiveRecord::Base.connected_to(role: :readonly) do
    assert_equal 3, Home.count
  end
end
```

The home inserted in the beginning of the test can't be read by the
replica database because when the test is started a transasction is
opened byy `setup_fixtures`. That transaction remains open for the
remainder of the test until we are done and run `teardown_fixtures`.

Because the data isn't actually committed to the database the replica
database cannot see the data insertion.

I considered a couple ways to fix this. I could have written a database
cleaner like class that would allow the data to be committed and then
clean up that data afterwards. But database cleaners can make the
database slow and the point of the fixtures is to be fast.

In GitHub we solve this by sharing the connection pool for the replicas
with the primary (writing) connection. This is a bit hacky but it works.
Additionally since we define `replica? || preventing_writes?` as the
code that blocks writes to the database this will still prevent writing
on the replica / readonly connection. So we get all the behavior of
multiple connections for the same database without slowing down the
database.

In this PR the code loops through the handlers. If the handler doesn't
match the default handler then it retrieves the connection pool from the
default / writing handler and assigns the reading handler's connections
to that pool.

Then in enlist_fixture_connections it maps all the connections for the
default handler because all the connections are now available on that
handler so we don't need to loop through them again.

The test uses a temporary connection pool so we can test this with
sqlite3_mem. This adapter doesn't behave the same as the others and
after looking over how the query cache test works I think this is the
most correct. The issues comes when calling `connects_to` because that
establishes new connections and confuses the sqlite3_mem adapter. I'm
not entirely sure why but I wanted to make sure we tested all adapters
for this change and I checked that it wasn't the shared connection code
that was causing issues - it was the `connects_to` code.

Add missing keys to ActiveSupport#instrumentation guide [skip ci]

Only define attribute methods from schema cache

Don't need to specify the version because Bundler 2.0 released.
Ref: https://bundler.io/blog/2019/01/03/announcing-bundler-2.html