minor fix for #16846

Merge pull request #16846 from prathamesh-sonpatki/document-error-handling-in-transactions-callbacks

Update upgrading guide about error handling in transactional callbacks [ci skip]

- Part of 16576
- [ci skip]

Remove extra 'has been' from deprecation warning about asserting selectors

[ci skip]

Remove extra 'has been' from the deprecation message

- [ci skip]

Add docs for web-console to 4.2 Upgrade Guide

Memoizing will not make possible to assert the output of the view if it
is changed after the first assert_select call

Related with plataformatec/simple_form#1130 and rails/rails-dom-testing#15

disable migrations logging while running test cases for AR schema tests

Fix query with nested array in Active Record

Removing unused fake models

Cleanup SchemaDumper

* Add private method primary_key_for, which more clearly shows that the
expected return value is nil when a primary key is not found.

* Consistent whitespace
* Remove unnecessary parentheses

[guides] Use `match ..., via: :all` in the custom exceptions app [ci skip]

Using `get` results in an unexpected error page(returning empty body) for requests of other HTTP mehtods other than GET. Use `match ..., via:
:all` so the exceptions app can be more stable.

Continuation of c9a43126

😢

Add support for Rack::ContentLength middelware

`User.where(id: [[1,2],3])` was equal to `User.where(id:[1, 2, 3])`
in Rails 4.1.x but because of some refactoring in Arel this stopped
working in 4.2.0. This fixes it in Rails.

[Dan Olson & Cristian Bica]

This fixes <"SQLite3::SQLException: no such column: legacy_things.person_id: SELECT \"legacy_things\".* FROM \"legacy_things\" WHERE \"legacy_things\".\"person_id\" = ?">
in OptimisticLockingTest#test_lock_destroy

fix the undefined method content_tag #15245

Deprecate implicit AD::Response splatting and Array conversion

not required include ActionView::Helpers::TagHelper in test as well

[Postgresql tests] Added enable_extension! to helper

Callback order in Active Record objects are important. Users should not
define callbacks before the association definition or surprising
behaviours like the described at #3798 will happen. This callback order
dependency is documented at https://github.com/rails/rails/blob/31bfcdc77ca0d8cec9b5fe513bdc6f05814dd4f1/activerecord/lib/active_record/associations.rb#L1222-1227.

This reverts #15728.

Fixes #16620.