Merge pull request #15618 from JuanitoFatas/doc/action-mailer-guide

[ci skip] Refine Action Mailer guide.
[ci skip] Fix doc for javascript_helper
Correct Bundler link [ci skip]
Merge pull request #15620 from aditya-kapoor/correct-bundler-link

Correct Bundler link [ci skip]
No need to decorate columns twice

We never want result types to override column types, and
`decorate_columns` can only affect column types. No need to go through
the decoration multiple times, we can just exclude the column types from
the result types instead.
Merge pull request #15619 from aditya-kapoor/fix-js-doc

[ci skip] Fix doc for javascript_helper
Merge pull request #15621 from sgrif/sg-column-type-decorations

No need to decorate columns twice
remove deprecated code. Rely on `describe` provided by minitest
Add test cases for #in? and #presence_in
begin refactoring add_constraints by moving join keys

add_constraints is complicated and difficult to read. This is the
beginning of a long process of refactoring this code. First step:
moved the join keys out of AssociationScope and into reflection.

We then don't need to call `reflection` because now reflection is
`self`.

`foreign_key` must be named something else because reflection already has a
`foreign_key` method and when passed into `JoinKeys` it was getting the
wrong assignment. `reflection_foreign_key` seemed to be an appropriate name.
I also named `key` `reflection_key` to match `reflection_foreign_key`.
use name specified by 'as' for automatic inverse association to avoid reflecting on wrong association
add missing changelog entry. refer [#16db90d] [ci skip]
Merge pull request #15635 from kuldeepaggarwal/add-missing-changelog

add missing changelog entry. refer [#16db90d] [ci skip]
fix typo in changelog [ci skip]
Fix Apache Directives [ci skip]

Directives need to be placed on their own lines in order to work. Tested on: `Server version: Apache/2.2.22 (Ubuntu); Server built:   Mar 19 2014 21:11:15`
Merge pull request #15636 from hundredwatt/patch-1

Fix Apache Directives [ci skip]
cleanup, get rid of trailing whitespace. [ci skip]

Follow up to #15636.

/cc @hundredwatt
Remove deprecation warning
Ensure `column_types` returns a type object, and not a column
Remove YAML serialization workaround for columns

We are no longer including column objects in YAML serialization, thanks
to https://github.com/rails/rails/pull/15621