Co-authored-by: qcorradi <q.corradi22@imperial.ac.uk>
Co-authored-by: Zachary Snow <zach@zachjs.com>

* Fixing a bug where always_* are not converted when attributed
* Added tests and updated Changelog for the attributed always_* fix

- The deleted chunk in TFBlock has been unreachable since 57ef23ef. The
  RemoveComments change would make it reachable by dropping the leading
  Null in a task or function body.
- The optimization in TFBlock was unsound because the nested block could
  shadow identifiers used (but not defined) in the tail of the outer
  block.
- The optimization is not clearly necessary, so I'm dropping it for now.
- Expand tf_block test coverage.

These are now kept while still supporting optional trailing commas and
without introducing pass-through inconsistencies.

- fold string literal comparisons
- fold non-decimal bit shifts
- fold non-decimal integer comparisons
- fold decimal bitwise AND and OR
- simplify cast expressions before elaboration
- remove duplicate cast expression traversal
- flatten concatenated numbers in a single pass

The implicit type of a localparam is not always needed. This improves
performance when complex localparam expressions are processed.