gh-152100: Move re compiler optimizations to Lib/re/_optimizer.py

Move the compile-time optimizations (_optimize_charset, _compile_charset,
_simple, _compile_info and the literal/charset prefix helpers) out of
_compiler.py into a new Lib/re/_optimizer.py.  _compiler.py keeps only the
bytecode emitter and imports them.  This is groundwork for a follow-up
optimization; there is no behavior change.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: serhiy-storchaka