Remove `FormBuilder` deprecation warning about block argument and tests

remove deprecated `assert_present` and `assert_blank`.

Remove deprecated `:distinct` option from `Relation#count`.

Change Rails Migration generator module to use AS::Concern

Removed deprecated methods partial_updates and family

Removed deprecated methods `partial_updates`, `partial_updates?` and
`partial_updates=`

Removed deprecated scoped method

Conflicts:
	activerecord/CHANGELOG.md

Removed deprecated default_scopes?

s/plugin_new/plugin

Using ActiveSupport::Concern instead of plain regular Ruby hooks in railties/lib/rails/generators/migration.rb file

Remove redundant escapes from xml serialization test

Further clean-up of ActiveSupport::Callbacks

In #11195 I noticed a trailing comma in the docs, but I decided to
further clean it up.

What I have done:

* Clean up the trailing comma in the docs and some extra whitespace
  lines.
* Used `Array#extract` options to factor the repetitive pattern of
  `args.last.is_a(Hash) ? ...`
* Renamed the local var `config` to `options` in `define_callbacks`, as
  `options` seems to be the de facto name for the options objects.
* Renamed the local var `l` to `line` in `define_callback` (maybe it
  meant `lambda` in the context) as single `l` may look like `1` in some
  fonts.

Created way of cloning a Rails::Application instance

There are historical reasons that the `plugin` command was `plugin_new`, now those are no longer applicable, we should remove the naming edge case from the project. This PR is based off of comments from #11176

ATP Railties

This change provides the ability to create a new application with a
configuration which can be specified.

updated AS:Callbacks docs, variable namings

Using preferred find_by syntax in guides

Adding find_by in guide to methods that trigger after_find

_ Rename the define_callbacks params to `names`
  - in order to match the naming conventions for `get_callbacks` and `set_callbacks` at https://github.com/rails/rails/blob/master/activesupport/lib/active_support/callbacks.rb#L736-743
  - `define_callbacks` just register names(events), not define the real callback functions.
- Rename the `reset_callbacks` params

Store a symbol directly inside DISPATCH_CACHE for additional roflscale

Remove evals from AM::Validations::Callbacks

Synchronize PostController#create code from 5.6 to others sections in Getting Started guide.

follow the same refactor at a63a964a

Fixed `permit` using for comments.

Remove a duplicated section [ci skip]