gh-152100: Support set operations in character classes (GH-152153)

gh-152100: Support set operations in character classes (GH-152153)

Implement set difference [A--B], intersection [A&&B] and union [A||B] in
regular expression character classes (Unicode Technical Standard #18),
including nested, complemented and compound set operands.  Symmetric
difference [A~~B] remains reserved.

Also use the new syntax in the standard library (_strptime, textwrap,
doctest, pkgutil).

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>