Add One Shot Key callbacks (#4697)

Add One Shot Key callbacks (#4697)

* Added callbacks to one shot modifier changes

* Altered signature of callback functions

* Reordered the callback methods, shortened brief documentation

* Added One Shot Modifier callback documentation

* First attempt at unit tests

* Revert "First attempt at unit tests"

This reverts commit 5ec21a782202c0d74cf21cb852bd319f0c8b4842.

* Simplified oneshot function implementations

* Made clear_oneshot_locked_mods to be conform action_util.h, adhering to the (void) signature

* Made used datatypes for oneshot mods consistently unsigned integers

* Corrected callback to call clear callback when clear_oneshot_locked_mods is invoked

* Simplified oneshot equals statements

* Corrected return type and signature of get and set oneshot locked mods

* Consolidated one shot callbacks, added initial layer callback version

* Fixed non-updating one shot layer variable after timeout or other clear, added code comments

* Added better one shot key docs