Add documentation for add_flash_types [ci skip]

Document a little bit the ActionController::Flash::add_flash_types
class method.
Merge pull request #11394 from robin850/patch-8

Add documentation for add_flash_types [ci skip]
 #11381: Ignore config.eager_load=true for rake

Closes #11381
Merge pull request #11389 from jetthoughts/11381_fix_hit_database_on_precompile

 #11381: Ignore config.eager_load=true for rake
Only raise DelegationError if it's is the source of the exception

This fixes situations where nested NoMethodError exceptions are masked
by delegations. This would cause confusion especially where there was a
problem in the Rails booting process because of a delegation in the
routes reloading code.

Fixes #10559
Add missing require
Fix a grammatical error/typo in Active Record Associations guide.
Merge pull request #11400 from dpdawson/master

Fix a grammatical error/typo in Active Record Associations guide. [ci skip]
Documment config.log_formatter added on 51aeae91

[ci skip]
Improve Active View Overview guide. [ci skip]
Merge pull request #11401 from dpdawson/master

Improved Active View Overview guide. [ci skip]
move `MissingHelperError` out of the `ClassMethods` module.
add test-case to verify `error.path` when a helper was not found.

This verifies the code added with:
https://github.com/rails/rails/commit/99c9d18601539c7e7e87f26bb047add1f93072af
Typo fix [skip ci]
Merge pull request #11414 from ankit8898/typo

Typo fix [skip ci]
Removing Gem.source_index [ci skip]
Merge pull request #11417 from arunagw/gem_source_index_no_required

Removing Gem.source_index [ci skip]
Remove update:application_controller rake task.
Merge pull request #11420 from simi/remove_update_application_controller_task

Remove update:application_controller rake task.
Remove block argument from callback example.

[ci skip]