Fix IRB deprecation warning on tab-completion

`lib` isn't autoloaded in most applications and I wouldn't recomment
storing test helpers there even if it was.

This was brought up in #38343. I think the original author meant to
write `test/lib`. I updated the docs to say to use either `test/lib` or
`test/test_helpers` (personally I prefer the latter).

Ref https://github.com/ruby/ruby/pull/2857.

Force connected_to to load the records if it's a Relation

Regexp-escape table name for MS SQL

I'm not sure why #38316 includes this partly change for #36589, but I
suspect that is to sync method signature for the previous backport which
wrongly changed the `remove` method signature.

https://github.com/rails/rails/commit/9a400d808bdbebd5ea50cebc79bde591d2669017#diff-21d4fbe002689dc4b0ab29f021585457R624

That was not intended, so I'll revert both changes in 6-0-stable.

#37168 is not backported to 6-0-stable.

[ci skip]

Expose `klass.default_scoped` as public API

Fix fallout from recent back ports

* there's no connection_db_config in Rails 6.0
* remove_column and friends "options" changes.
* merge conflict markers in activerecord/CHANGELOG.md

Noticed while running tests for JRuby's AR-JDBC. While the Rails tests
where running fine, our local ones broke during migration tests.
Fixes are basically from master.

Fixes #38315

Move advisory lock to it's own connection

Fix keyword arguments warnings in Active Job

Cache compiled view templates when running tests by default

https://buildkite.com/rails/rails/builds/64281#b6f8859b-ee39-40d7-8f0a-d0ba78efbf03/1001-1012
https://buildkite.com/rails/rails/builds/66563#e059e1ba-a5b1-4a8f-a634-417d32d7f238/1016-1027

This reverts commit 80e72c5e, reversing
changes made to 0dad1e3e.

Follow up 5572df92.

Otherwise it is hard to invert non-kwargs method to kwargs method.

This makes table and column options to be synchronized as kwargs.

`add_foreign_key`'s arguments are compatible (invertable) for `remove_foreign_key` without customize

So the custom `invert_add_foreign_key` is a little redundant.

Fix keyword arguments warnings in Active Job

Remove an empty line from generated migration

Fix CI failures due to MySQL 8.0.19 no longer output integer display width unless ZEROFILL is also used

https://buildkite.com/rails/rails/builds/66475#7a6c54bc-4ed3-4676-b196-4fee031f43bf

Fixes #38226.

`helper_method` was taking `**kwargs` on all definitions by default.
ruby will assume that this means you want keyword args and call
`to_hash` on what you pass if the object responds to `to_hash`. Instead
we should only take keyword args if the helper method defined intends
to pass keyword args.

This also fixes a warning when you pass a hash to your helper method,

```
warning: Using the last argument as keyword parameters is deprecated; maybe ** should be added to the call
```

Also, this would be a good candidate for using `...`, but since `send`
requires the method as the first argument, we can't use it here.

https://bugs.ruby-lang.org/issues/16485
https://github.com/ruby/ruby/pull/2832

https://buildkite.com/rails/rails/builds/66424#a1fdb92a-a9a0-4ff2-afc8-a59410cd4fdf/1016-1027

The intent of that tests is completely covered by with order version.

https://github.com/rack/rack/compare/2.1.0...2.1.1

Fix CI error with minitest 5.14

rack 2.1.0 changed expires date format from rfc2822 to httpdate