YAPF 2: Replatform off of lib2to3 to libcst and structured pattern matching (2025 project idea)

[Spitfire1900]

YAPF migrated to a fork of lib2to3 as _ylib2to3 in order to patch in support for 3.10 features like structured pattern matching.

Maintaining the fork of lib2to3 as a long term project to implement 3.12+ new language features insn't feasible and should consider a separate concrete syntax tree (CST) provider like libcst.

This year also marks the EoL of Python 3.9, so structured pattern matching will be available in all supported versions of Python come November; this re-platforming effort may take advantage of that also.