Use strip_heredoc where possible

Following up on an observation by @rafaelfranca

https://github.com/rails/rails/pull/10170/files#r3753963

Reduce the number of gsub calls to the two cases where inputs are concatenated
from various sources and with inconsistent indentation.

Also zap extraneous spacing from the sass-rails line... presumably this is a
holdover from a previous time where this aligned the version string with an
adjacent line.
Fix StatementCache docs format [ci skip]
Fix links containing stray colons
minor edit on StatementCache documentation [ci skip]
Update to Ryan's new book per his suggestion

See https://github.com/lifo/docrails/commit/edeb98c2745cbf29725eca87332cefb4f273986a#commitcomment-2995521
Fix a typo
Extract method declaration regexp into a constant
Merge pull request #10194 from pabloh/extract_regexp_at_generators_testing_assertion

Extract method declaration regexp for assert_method into a constant
Revert "Merge pull request #10194 from pabloh/extract_regexp_at_generators_testing_assertion"

This reverts commit 81f243375b9d3cfd431c1ca904c5c1efc9a41ae8, reversing
changes made to c7673b0981d961e5510c85d958c944876d543314.
fix :nodoc: mark on AR::AttributeMethods::Serialization [ci skip]
complete rewrite of the documentation of AS::PerThreadRegistry

* It focuses on how to use it.

* Removes some ambigueties in the original docs about whether the state is stored in the class.

* Documents it provides class-level accessors via method_missing.

* Documents that if the extended class has an initializer, it must accept no arguments.
simplifies the RDoc of AR::RuntimeRegistry

The previous version was kind of duplicating the documentation of
AS::PerThreadRegistry. Just say how to use it, the thread locals
registry is know part of our vocabulary (though a pointer to
Active Support is added for reference).
removes calls to AR::Runtime.instance

Registries have class-level accessors to write clean code, let's
use them. This makes style uniform also with existing usage in
ScopeRegistry and InstrumentationRegistry.

If performance of the method_missing callback was ever considered to
be a concern, then we should stop using it altogether and probably
remove the callback. But while we have the feature we should use it.
remove unused variable
Merge pull request #10201 from vipulnsward/remove_unused_var_in_guides

remove unused variable
hides the per thread registry instance, and caches singleton methods

Existing code was delegating to the instance with delegate
macro calls, or invoking the instance method to reach
the object and call its instance methods.

But the point is to have a clean class-level interface where
the thread local instance is hidden in the implementation.

References #11c6973.
References #10198.
update git links
Merge pull request #10204 from shmatov/update-git-links

Update github links
Corrected paramter to parameter
Add :nodoc: mark to PerThreadRegistry#method_missing [ci skip]