CLI: Add 'cd' subcommand (#12584)

* CLI: Add 'cd' subcommand

Go to your qmk_firmware dir with ease.

* Fix for Windows and do not run if already under QMK Home

* Make flake8 happy

* Fix prompt for Windows

* Make flake8 happy once again

* I'll get it right eventually

* Apply suggestions from code review

Co-authored-by: Ryan <[email protected]>

* Add subcommand to __init__.py and fixup after rebase

* Update Windows code to use milc's run

* Unify the subshell starting with os.execl

* Exit with error msg when output is redirected to non-TTY.

* Revert Windows-specific code

Co-authored-by: Ryan <[email protected]>

lib/python/qmk/cli/__init__.py

@@ -31,6 +31,7 @@ safe_commands = [
 subcommands = [
     'qmk.cli.bux',
     'qmk.cli.c2json',
+    'qmk.cli.cd',
     'qmk.cli.cformat',
     'qmk.cli.chibios.confmigrate',
     'qmk.cli.clean',