Display diagnostics in text format for xhr request
Use inheritance chain instead of callbacks to increment counter caches after create
Use inheritance chain instead of callbacks to increment counter caches after destroy
The Association Relation should use `empty?` and `size` from Relation.

968c581ea34b5236af14805e6a77913b1cb36238 have introduced this bug #14744
on Association Relation when the method `empty?` or `size` was called.

Example:
  # Given an author that does have 3 posts, but none of them with the
  # title 'Some Title'
  Author.last.posts.where(title: 'Some Title').size
  # => 3

It was occurring, because the Association Relation had implemented these
methods based on `@association`, this way giving wrong results.

To fix it, was necessary to remove the methods `empty?` and `size` from
Association Relation. It just have to use these methods from Relation.

Example:
  # Given an author that does have 3 posts, but none of them with the
  # title 'Some Title'
  Author.last.posts.where(title: 'Some Title').size
  # => 0
  # Now it will return the correct value.

Fixes #14744.
Make sure the column_name is different from 'all'.

968c581ea34b5236af14805e6a77913b1cb36238 have fixed the EagerLoadTest, but
not in the correct way.

The problem was when `empty?` or `size` was called on relation. It was
triggering `count(:all)`, which was passing `:all` as the column name to `count`
on Calculations.

On the other hand, the method `calculate` on Calculations was calling
`construct_relation_for_association_calculations` instead of `perform_calculation`,
because `has_include?` was returning `true` since `column_name` was present.

To prevent calling the wrong method to perform the calculation, we have to check
if the `column_name` is present and if it is different from `:all` (which is now used
to correctly do `count` with `select`).

More information here: https://github.com/rails/rails/commit/968c581ea34b5236af14805e6a77913b1cb36238#commitcomment-6006135
[ci skip] Add missing end in one of the examples in Migrations.md.
Merge pull request #14758 from JuanitoFatas/migrations-md

[ci skip] Add missing end in one of the examples in Migrations.md.
use YAML.load_file in database tasks example

rather than YAML.load(File.read(path)). YAML.load_file is also used in
guides/rails_guides/helper.rb since 2011, the only other precedent I could find.
Merge pull request #14756 from laurocaetano/fix-count-on-association-relation

Fix count on association relation (calls to empty and size).
Merge pull request #14762 from dwo/master

use YAML.load_file in database tasks example
Merge pull request #14745 from razum2um/plain-text-diagnostics

Display diagnostics in text format for xhr request
Set _after_create_counter_called flag to make update counter cache work
Restore the destroy_by_association check in post destroy counter cache
Hide BelongsToAssociation#increment_counters and #decrement_counters
Changed change_column in PG schema_statements.rb to make sure that the uuid_generate function was not being quoted.
Merge pull request #14766 from eric-chahin/migration_bug

Changed change_column in PG schema_statements.rb to make sure that the u...
Merge pull request #14765 from byroot/refactor-counter-cache-create-and-destroy

Refactor counter cache create and destroy
Add CHANGELOG entry for #14766 [ci skip]
Update AC::Metal documentation example [ci skip]

Include proper module since AV was extracted form AP as mentioned in #14659.
Merge pull request #14768 from spectator/ac_metal_docfix

Update AC::Metal documentation example