Allow ActionDispatch::Response to be autoloaded

Merging multiple Hashes in Ruby < 2.6 is so hard...

Fix typo in activestorage README [ci skip]

`a ActionDispatch::Http::UploadedFile object` ->
`an ActionDispatch::Http::UploadedFile object`

Similar to b744372f, this defers loading
`ActionDispatch::Response` until after initialization, which will allow
applications to boot a bit faster in development but also paves the way
for `return_only_media_type_on_content_type` to work correctly when set
from `new_framework_defaults_6_0.rb`.

Benchmark:

    $ cat test.rb
    require "bundler/setup"
    before = ObjectSpace.each_object(Module).count
    start = Process.clock_gettime(Process::CLOCK_MONOTONIC)
    require "action_controller"
    finish = Process.clock_gettime(Process::CLOCK_MONOTONIC)
    after = ObjectSpace.each_object(Module).count
    puts "took #{finish - start} and created #{after - before} modules"

Before:

    $ ruby test.rb
    took 0.35654300000169314 and created 608 modules

After:

    $ ruby test.rb
    took 0.2770050000108313 and created 466 modules
Co-authored-by: NSerena Fritsch <serena@intercom.io>

Fix typo and simplify autoload paths intro

Initially I just wanted to remove _to_ from _We call autoload paths to
the list..._. But this sentence also seemed a little bit overcomplicated
😅

[ci skip]

Allow Sidekiq access to the underlying Job class

Fix a typo in DatabaseTasks#current_config

This commit fixes a method typo that was introduced in #37199, also also
adds tests for the `DatabaseTasks#current_config` method given it's
current implementation.

While I was in here, I also made it so that if `current_config` is
called with an `env` it won't try to look up the `Rails.env`
potentially resulting in an error for non-Rails application.

IMO this method should be deprecated & removed as it's no longer used in
Rails, is confusing (for example: `test_current_config_read_after_set`),
and is currently dependent on Rails if `env` isn't passed.
Co-authored-by: Neileencodes <eileencodes@gmail.com>

Fix typo in ActionMailbox::InboundEmail::MessageId [ci skip]

- `a Active Storage` -> `an Active Storage`
- `which be uploaded` -> `which is uploaded`

Caused by #37120.

Co-authored-by: NJian-Long Huang <huang@jianlong.org>

This broke CI. https://buildkite.com/rails/rails/builds/63708

Fixes #36956 by dup'ing the value and entry object returned from MemoryStore.

[ci skip] Note removal of `render :text` & `:nothing` options from 5.1 upgrade guide

This just makes it explicit that the deprecated :text option is
completely removed in Rails 5.1

Currently `wrapped` is a String.  Instead pass Class so that Sidekiq can get access to the ActiveJob and its configuration without having to constantize.  I verified that `JobClass.to_s` == `"JobClass"` so serialization to JSON should not be affected.

```ruby
> JSON.dump({"wrapped" => SomeJob})
=> "{\"wrapped\":\"SomeJob\"}"
```

By having access to the ActiveJob class, Sidekiq can get access to any `sidekiq_options` which have been set on that ActiveJob type and serialize those options into Redis.

https://github.com/mperham/sidekiq/blob/master/Changes.md#60

Fix has_one through reflection casting check

Remove Capistrano from asset pipeline guide

Reduce surface area of ConnectionSpecification

This is the conventional name for that parameter.

Expand on helpers available in Action Mailer

Remove 'now just' — document the current state in an accessible way. Make it clear the set of helpers isn't **exactly** the same

Add references to `mailer` and `message` helpers which can be very useful.

`attachments` is already covered in "Making Inline Attachments"

Finding the mail-specific formatting heleprs are