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

**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")`.