UTF-8 Mode: TextIOWrapper.reconfigure should support `encoding="locale"`

[methane]

Feature or enhancement

TextIOWrapper.__init__() supports encoding="locale" option.
But TextIOWrapper.reconfigure() doesn't support it yet.

Pitch

Scenario:

Users may set PYTHONUTF8=1 enviroment variable but want to use locale encoding for stdin/stdout.

They may want to do sys.stdout.reconfigure(encoding="locale").