Smallish overhaul of Auto-Shift feature (#6067)

Smallish overhaul of Auto-Shift feature (#6067)

* Fix edge case when using One Shot Layer with Auto Shift, and it not triggering the cleanup
* Remove junk code (no longer used)
* Replace `(un)register_code` calls with `tap_code` where appropriate
* Fixed up Switch check to be more readable (less verbose)
* Simplified modifier check (if it comes back non-zero, there are mods)
* Add additional function calls for autoshift settings
* Made all variables static, since there are function calls to get their status
* Fixed up documentation
* Re-add special characters that were missed
* formatting pass