Added method `#eql?` to `ActiveSupport::Duration`, in addition to `#==`.

Currently, the following returns `false`, contrary to expectation:

    1.minute.eql?(1.minute)

Adding method `#eql?` will make this behave like expected. Method `#eql?` is
just a bit stricter than `#==`, as it checks whether the argument is also a
uration. Their parts may be different though.

    1.minute.eql?(60.seconds)  # => true
    1.minute.eql?(60)          # => false
Update RecordNotFound exception cases to include a message with the
Model that the Record was not found in.
A warning line should look like a warning section

[ci skip]
Add a note on custom validation contexts.

The documentation on `:on` for validations was inconsistent, and most
only referenced the `:create` and `:update` contexts. I fixed those to
be consistent with the documentation on `AM::Validations.validates`,
which seemed to have the best docs.

[ci skip]
[ci skip] add guide for ActiveModel::SecurePassword
Roll back open transactions when the running thread is killed.
'Reversible' ->active_record_migrations [ci skip]

Reversible method documentation moved from migrations.md  to active_record_migrations.md
'Revert' ->active_record_migrations [ci skip]

Revert method documentation moved from migrations.md  to active_record_migrations.md
[ci skip] Fix some typos, normalize sentence.

Follow up of #16722.

https://github.com/rails/rails/pull/16722

also normalize all instance gained methods’ sentence.
Changed the DangerousAttributeError exception message to include messaging that the conflict could be because of a conflicting attribute.
Explain ERB space removal. [ci skip]
Changes default render behavior from file to template.
Merge pull request #16669 from aantix/dangerous_attribute_error_better_message

Improved the error messaging for the DangerousAttributeError exception
Change ActiveJob test directory to "test/jobs"
Merge pull request #16908 from y-yagi/change_activejob_test_dir

Change ActiveJob test directory to "test/jobs" [ci skip]
use `allow_blank` option instead
Revert "Merge pull request #15312 from JuanitoFatas/action_view/asset_path"

This reverts commit 21ec7fefea5a1b823cb88733b019b3d52240801d.

Per #16911, there's actually a good reason for a "blank" value to have a
useful `to_s` here. So let's also add some tests to prove that.
Merge pull request #13656 from chanks/rollback_transactions_in_killed_threads

Data corruption risk: Roll back open transactions when the running thread is killed.
Merge pull request #16910 from kuldeepaggarwal/use-rails-options

use `allow_blank` option instead of custom condition
form_helpers: demonstrating there is also a collection_select method in form builder