Refactor function to make it less verbose and simpler to change: error cases first, then special cases, then normal behaviour.

Make code more readable by changing the order of a condition and moving the simple return case first.

For example, if they're called on entry/exit to a decorated function they pick up the directives.
They should really be independent of most user defined settings, especially local ones.

Add --skip-interpreter option to cygdb

* Fix class attributes access where cpp_locals=False.
* Add "no-cpp-locals" tag to mark a test as not suitable for running with "cpp_locals=True".
* Add a list of "extra_directives" to runtests as additional test mode.

Resolves some issues in https://github.com/cython/cython/issues/4266

Seems a remanant of an earlier implementation, but generator expressions *never* use "GeneratorExpressionScope" and in fact it's only used for comprehensions.

Set the "is_target" attribute for names, attributes and temps (anything name-like) to preserve that information for later pipeline steps.

Avoid going through an attribute assignment for an intermediate node result since it may not be the end result.

Closes https://github.com/cython/cython/issues/4268

Closes https://github.com/cython/cython/issues/4268

To be used in https://github.com/cython/cython/pull/4241

See https://github.com/cython/cython/pull/3626

Closes https://github.com/cython/cython/issues/4172