bundle exec db:migrate rake was not working, with the new runner, before this commit

`bin/rails test` runner (rerun snippets, run tests by line, option documentation)

Add a new-line to the end of route method generated code.

ActiveRecord: Add a changelog entry for issue #17680. [ci skip]
Conflicts:
	activerecord/CHANGELOG.md

Active Record changelog pass [skip ci]

[ci skip] use true as value rather than symbol

[skip ci] Fixed typo in asset pipeline documentation

[ci skip] use false as value rather than symbol

Change commands in the Getting Started guide to use scripts in bin/ [ci skip]

[ci skip]

Fix regression on route method that was added by
bac812a7. The regression was that when
calling the `route` method, we were not appending a \n anymore.

[fixes #19316]

This is a better test for 51660f01. It is testing that the SQL is the
same before and after the previously leaky scope is called. Before if
`hotel.drink_designers` was called first then `hotel.recipes` would
incorrectly get the scope applied. We want to be sure that the
polymorphic hm:t association is not leaking into or affecting the
SQL for the hm:t association on `Hotel`.

The reason I couldn't do this before was because there was an issue with
the SQL getting cached and wanted to resolve that later and then fix the
test to be better. Because of the caching, this test requires that
`Hotel.reflect_on_association(:recipes).clear_association_scope_cache`
be called after the first call to `hotel.recipes` to clear the
assocation scope chain and not interfere with the rest of the test.

In the tests if I were to call `post.categorizations.to_a` and then later call
`post.categorizations.to_a` expecting to have different results the 2 queries
would be the same because of the caching involved in
`@association_scope_cache`. The chain gets cached and the queries will
be the same even if they are not supposed to be (i.e. testing an order
dependent scoping issue).

I found this issue because I was working on a bug with cached scoped
in hm:t and hm:t polymorphic relationships but `capture_sql` was
outputting the wrong SQL to write a good test.

Remove gem check in guides/rails_guides.rb

Conflicts:
	guides/rails_guides.rb

This logic was just doing duplicated work, since the button_to helper
relies on tag/content_tag to generate the button html, which already
handles all boolean attributes it knows about.

The code dates back to 2005: 43c470fa.

Reuse the CollectionAssociation#reader proxy cache if the foreign key is present from the start.

Conflicts:
	activerecord/CHANGELOG.md

Make example code consistent for better understanding. [ci skip]

Update old link in pessimistic.rb comments [ci skip]