Tidy up and tighten deprecation skips

Problem/Motivation

We skip a number of deprecations in .deprecation-ignore.txt but some of these are outdated or could be tightened up.

For example:

%The "Symfony\\Component\\Validator\\Context\\ExecutionContextInterface::.*\(\)" method is considered internal Used by the validator engine\. (Should not be called by user\W+code\. )?It may change without further notice\. You should not extend it from "[^"]+"\.%

This doesn't seem to trigger any more.

%Method "Twig\\NodeVisitor\\NodeVisitorInterface::[^"]+" might add "[^"]+" as a native return type declaration in the future. Do the same in (child class|implementation) "[^"]+" now to avoid errors or add an explicit @return annotation to suppress this message%

Any implementation in contrib would also skip this deprecation - but we want contrib to add return types now, so core can add them in the future when Twig also does. We can tighten this up so it only triggers on the core implementation.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet