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.
'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.
Explain ERB space removal. [ci skip]
Changes default render behavior from file to template.
form_helpers: demonstrating there is also a collection_select method in form builder
Singular credit_card controller name changed to plural
Use dynamic path for dummy app location in plugin's test_helper.rb
Stop nil checking on safe_append=

ERB compiler guarantees safe_append= will be called with a string, so
nil checks don't make sense.  Anything else calling this method should
check for nil themselves before calling
Pare down and simplify Active Job's rake tasks
Tighten up AJ::Arguments and its tests

* Disallow deserialization of non-primitive objects
* Broaden coverage; remove superfluous tests
simplify test_adapter
Merge pull request #16918 from kiuru/master

Singular credit_card controller name changed to plural [ci skip]
Merge pull request #16920 from seuros/aj

simplify test_adapter
handle <%== nil %> cases

This is much less common than string literal appends, so add a special
case method for it.  Maybe fixes bug reported by @jeremy on 97ef636191933f1d4abc92fc10871e6d1195285c
Add `test:jobs` task
Merge pull request #16922 from y-yagi/add_test_jobs_task

Add test jobs task
add implementation of respond_to? for ActiveSupport::Duration