`changed_attribute_names_to_save` is called in `keys_for_partial_write`,
which is called on every save when partial writes are enabled.

We can avoid generating the full changes hash by asking the mutation
tracker for just the names of the changed attributes. At minimum this
saves one array allocation per attribute, but will also avoid calling
`Attribute#original_value` which is expensive for serialized attributes.

Fix leftover references to VariantsController in AS documentation [ci skip] 

VariantsController has been merged to RepresentationsController, this
PR fixes outdated references to VariantsController in ActiveStorage documentation.

Mocha updates

Because this class includes not only `assert_difference` but also tests
of other assertion methods.

Enable verbose option in ActiveStorage

rewords a bit RDOC_MAIN.rdoc [ci skip]

* Same change as bba832d4

[LinkedRach, Daniel Colson, Xavier Noria]

Update URLs in RELEASING_RAILS.md [ci skip]

* Use https instead of http with URI scheme for Travis
* Update Url for "Agile Web Development with Rails"

Mocha v1.5.0 is currently the latest release.

This has been possible since Mocha v1.0 and makes it clear that we want
Mocha to integrate with Minitest, not Test::Unit.

The `require: false` option hasn't been needed since Mocha v1.0.

Fix `actionview/CHANGELOG.md`

[ci skip]

- Add missing dots at the end of sentences.
- Wrap RecordTagHelper into `.
- `RecordTagHelper` => `ActionView::Helpers::RecordTagHelper`.

[ci skip]

Remove RecordTagHelper

Use an ActiveSupport::CurrentAttributes model to provide the host for service urls

* Since #18411, we started to inform about extracted gem (record_tag_helper)
  to developers who use `ActionView::Helpers::RecordTagHelper` 's methods.

* Currently, it seems no problem that we don't have to support no longer.

The `Capybara.server=` proc acceptance restored in Capyara 3.0.1.
Ref: https://github.com/teamcapybara/capybara/commit/8f115d94e035eca992036f16e50c1dce5f555c97

Trying to pass the current request down to the service so that it can
create full urls instead of paths makes the API messy so use a model
based on ActiveSupport::CurrentAttributes to provide the current host
to services that need it (primarily the disk service).

Before it was possible to for example use the direct upload controller
without using the site.

This way we don't need to remember which packages we need to install.

[ci skip] Add securing rails app guide link to credential section

* In 5.2 release note, added [securing rails app guide](http://edgeguides.rubyonrails.org/security.html#custom-credentials) link to [credentials section](http://edgeguides.rubyonrails.org/5_2_release_notes.html#credentials).

Bring back private class methods accessibility in named scope

`SetupAndTeardown#teardown` should call any subsequent after_teardown:

Fixes a bug in IE11 that broke ActiveStorage direct uploads

Add changelog entry for #32446

In #32446 was added method `dig` to `session`.
Improve docs of method `dig`.

[ci skip]

ccea4cf3 broke multiple database structure:dump, the current_config line
should have been deleted instead. I'm struggling to write a test for
this since the confings are passed from rake to the structure_dump
method rather than the other way around. Hoping to come up with a test
while I work on structure:load commands for multiple databases.

Fix test added in #32444

It seems that it is no longer possible to specify the value held by
`Capybara.server` as sever.

Ref: https://github.com/teamcapybara/capybara/commit/ba7674086cbcd3b22d3614011815bc5d483e5960

Currently test `#test_logger_does_not_mutate_app_return` doesn't
test mutation of response and the test passes with and without changes
added in #32444. `#freeze` response in the test in order to
test mutation.

All of Date, DateTime and Time respond to `iso8601`.

  If you have a regular test that have a teardown block, and for any reason an exception get raised, ActiveSupport will not run subsequent after_teardown method provided by other module or gems.
  One of them being the ActiveRecord::TestFixtures which won't rollback the transation when the test ends making all subsequent test to be in a weird state.

  The default implementation of minitest is to run all teardown methods from the user's test, rescue all exceptions, run all after_teardown methods provided by libraries and finally re-raise the exception that happened in the user's teardown method.
  Rails should do the same.