This issue is caused by `@_trigger_update_callback` won't be updated due
to `_update_record` in `Locking::Optimistic` doesn't call `super` when
optimistic locking is enabled.

Now optimistic locking concern when updating is supported by
`_update_row` low level API, therefore overriding `_update_record` is no
longer necessary.

Removing the method just fix the issue.

Closes #29096.
Closes #29321.
Closes #30823.

Fixes #32129.

Remove extra arg passed to `Rails::Command::RoutesTest#run_routes_command`

Related to 6bd33d66

Deprecate safe_level of `ERB.new` in Ruby 2.6

### Summary

In a Rails application using Ruby 2.6.0-dev, when running `bin/rails g migration`
with `RUBYOPT=-w`, an ERB deprecation warnings will be displayed.

```console
% ruby -v
ruby 2.6.0dev (2018-03-03 trunk 62644) [x86_64-darwin17]
% bin/rails -v
Rails 6.0.0.alpha
% RUBYOPT=-w bin/rails g migration create_foos

(snip)

/Users/koic/src/github.com/rails/rails/railties/lib/rails/generators/migration.rb:66:
warning: Passing safe_level with the 2nd argument of ERB.new is
deprecated. Do not use it, and specify other arguments as keyword
arguments.
/Users/koic/src/github.com/rails/rails/railties/lib/rails/generators/migration.rb:66:
warning: Passing trim_mode with the 3rd argument of ERB.new is
deprecated. Use keyword argument like ERB.new(str, trim_mode: ...)
instead.
/Users/koic/src/github.com/rails/rails/railties/lib/rails/generators/migration.rb:66:
warning: Passing eoutvar with the 4th argument of ERB.new is
deprecated. Use keyword argument like ERB.new(str, eoutvar: ...)
instead.
      create    db/migrate/20180304002144_create_foos.rb
```

This PR suppresses the above deprecation warnings in Ruby 2.6.0-dev.

This warning is due to the interface of `ERB.new` will change from Ruby 2.6.

> Add :trim_mode and :eoutvar keyword arguments to ERB.new.
> Now non-keyword arguments other than first one are softly deprecated
> and will be removed when Ruby 2.5 becomes EOL. [Feature #14256]

https://github.com/ruby/ruby/blob/2311087b685e8dc0f21f4a89875f25c22f5c39a9/NEWS#stdlib-updates-outstanding-ones-only

The following addresses are related Ruby's commit.
https://github.com/ruby/ruby/commit/cc777d0

Also this PR will change `ERB.new` used in `tasks/release.rb`.

### Other Information

This PR uses `ERB.version` to switch `ERB.new` interface. Because Rails 6
supports multiple Ruby versions (Ruby 2.4.1 or higher), it need to
use the appropriate interface.

Using `ERB.version` instead of `RUBY_VERSON` is based on the following patch.
https://github.com/ruby/ruby/pull/1826

This patch is built into Ruby.
https://github.com/ruby/ruby/commit/40db89c0934c23d7464d47946bb682b9035411f9

Currently primary key value can not be updated if a record has a locking
column because of `_update_record` in `Locking::Optimistic` doesn't
respect `id_in_database` as primary key value unlike in `Persistence`.

And also, if a record has dirty primary key value, it may destroy any
other record by the lock version of dirty record itself.

When updating/destroying persisted records, it should identify
themselves by `id_in_database`, not by dirty primary key value.

The `host` and `port` can't use this context.

Convert the user to atheism by ditching the extra example that demonstrates
the same thing as date_of_birth.

Demonstrate the NoMethodError on date_of_birth first, then call age that
uses date_of_birth internally. Thus showing that accessing it publicly fails,
but using it internally succeeds.

Introduce explicit rails server handler option

Fix occurrences Fixnum|Bignum

Fix actionview tests execution

Related to https://github.com/rails/rails/commit/d4eb0dc89ee6b476e2e10869dc282a96f956c6c7#r27830891

On my local environment execution of `cd actionview/ && bin/test` raises error:

```
(snip)
rails/actionview/test/template/render_test.rb:6:in `<top (required)>': superclass mismatch for class TestController (TypeError)
```

In some test files `TestController` inherited from `ActionController::Base`,
but in `test/actionpack/controller/render_test.rb` file `TestController`
inherited from `ApplicationController`.
This produces error `superclass mismatch for class TestController (TypeError)`

Step to reproduce this on any environment:
`cd actionview/ && bin/test test/template/streaming_render_test.rb test/actionpack/controller/render_test.rb`

I mistype `rails server production` instead of `rails server -e
production` expecting to lunch a server in the production environment
all the time. However, the signature of `rails server --help` is:

```
Usage:
  rails server [puma, thin etc] [options]
```

This means that the `production` argument is being interpreted as a Rack
server handler like Puma, Thin or Unicorn.

Should we argue for the `rails server production`? I'm not sure of the
reasons, but the `rails console production` behavior was deprecated in:
https://github.com/rails/rails/pull/29358, so parity with the existing
`rails console production` usage may not hold anymore.

In any case, this PR introduces an explicit option for the Rack servers
configuration. The option is called `--using` (or `-u` for short) to
avoid the `rails server --server` tantrum.

The new interface of `rails server` is:

```
Usage:
  rails server [using] [options]

Options:
  -p, [--port=port]                        # Runs Rails on the specified port - defaults to 3000.
  -b, [--binding=IP]                       # Binds Rails to the specified IP - defaults to 'localhost' in development and '0.0.0.0' in other environments'.
  -c, [--config=file]                      # Uses a custom rackup configuration.
                                           # Default: config.ru
  -d, [--daemon], [--no-daemon]            # Runs server as a Daemon.
  -e, [--environment=name]                 # Specifies the environment to run this server under (development/test/production).
  -u, [--using=name]                       # Specifies the Rack server used to run the application (thin/puma/webrick).
  -P, [--pid=PID]                          # Specifies the PID file.
                                           # Default: tmp/pids/server.pid
  -C, [--dev-caching], [--no-dev-caching]  # Specifies whether to perform caching in development.
      [--early-hints], [--no-early-hints]  # Enables HTTP/2 early hints.
```

As a bonus, if you mistype the server to use, you'll get an
auto-correction message:

```
$ rails s tin
Could not find handler "tin". Maybe you meant "thin" or "cgi"?
Run `rails server --help` for more options.
```

Fix links in the psql guide [ci skip]

Merge Previews/Variants controller into one Representations controller.

Since ActiveStorage::Blob::Representable unifies the idea of previews and
variants under one roof as representation, we may as well have the
controllers follow suit.

Thus ActiveStorage::RepresenationsController enters the fray. I've copied
the old tests for both previews and variants and unified those as well.

This removes `|| id` which were added in #9963 and #23887 since it is no
longer necessary.

This reverts ignoring polymorphic error introduced at 02da8aea.

What the ignoring want to solve was caused by force eager loading
regardless of whether it is necessary, but it has been fixed by #29043.

The ignoring is now only causing a mismatch of `exists?` behavior with
`to_a`, `count`, etc. It should behave consistently.

This is an alternative of #29722, and follow up of #32048.

This does not change the current behavior, but makes it easier to modify
all polymorphic names consistently.

The `+` does not work if the string contains spaces.

Numeric#positive? and Numeric#negative? was added to Ruby since 2.3,
see https://github.com/ruby/ruby/blob/ruby_2_3/NEWS
Rails 6 requires Ruby 2.4.1+ since https://github.com/rails/rails/pull/32034

Ruby 2.4+ provides `Hash#compact` and `Hash#compact!` natively,
so `active_support/core_ext/hash/compact` is no longer necessary.

Since Rails 6 requires Ruby 2.4.1+.

https://bugs.ruby-lang.org/issues/12752
https://ruby-doc.org/core-2.4.0/String.html#method-i-unpack1

This comment was added at 070dda28. That arguments has already been
changed since those are internal nodoc classes, but the comment does not
reflect the current state.

I decided to remove the staled comment since it is not useful for
understanding what the class does.

[ci skip]

Follow up of b988ecb9.

This was added for internal usage, it doesn't need to be public.

Duplicated method name list is no longer needed.