Fixed duplicate subscribers in ActiveSupport::Subscriber

ActiveSupport::Subscriber no longer creates multiple subscribers when
you redefine a method.
Fix `Relation#delete_all` inconsistency

When relation scopes include one of `uniq`, `group`, `having` or
`offset`, the generated query ignores them and that causes unintended
records to be deleted. This solves the issue by restricting the deletion
when those scopes are present.

rails/rails#11985
Reuse the force_clear_transaction_record_state
prepend mutates the string so we can remove the assignment
Remove the assignment for real this time.

cc:
https://github.com/rails/rails/commit/a11e2fcff8cdc9691b977d8330abe63024f8c732#commitcomment-6353614
and 0369dbf
Merge pull request #15139 from zzak/habtm_build_model_name

Remove the assignment for real this time.
Remove unecessary require
Merge pull request #15140 from arthurnn/small_cleanup

Remove unecessary require
remove trailing whitespace. [ci skip]
doc, pg `hstore` and `json` columns are mapped as `Hash`. [ci skip]

Closes #15141.
Generate the cookies_serializer configuration with :marshal when upgrading

We were generating this configuration with :json what may break
applications upgrating from Rails 4.0-.

Now we always generate with a safer value and people is free to choose
hybrid if they want.

We don't generate with hybrid by default because there are some cases
that can fail. These cases are explained on the upgrading guide.
foo :bomb:
Merge pull request #15071 from leafac/issues/11985

Fix `Relation#delete_all` inconsistency
Add CHANGELOG entry for #15071 [ci skip]
Merge pull request #15037 from roccoblues/fix_duplicate_activesupport_subscribers

Fixed duplicate subscribers in ActiveSupport::Subscriber

Conflicts:
	activesupport/CHANGELOG.md
Replace first person point of view on guides.

[skip ci]
Merge pull request #15143 from htanata/first_person_pronouns

Replace first person point of view on guides.
Fix typo in CHANGELOG entry for #15071
Merge pull request #15144 from leafac/fix-changelog-#15071

Fix typo in CHANGELOG entry for #15071
fixed capitalizations [ci skip]

jQuery, SQLite3 and Unicorn use these respective capitalizations pretty much everywhere else in the comment sections of the project.