This is an inelegant hack for #2522 but makes things work. Basically we give `action.c` a chance to handle the hold event early so that we can swap the keyboard for later keys. Later, to allow the hold to happen again quickly we nuke the key record so that tapping is reset. I tried to find a cleaner way, honestly.
This protocol breaks out "duplicate" keys into their own entry in the packet so that more complicated logic can be done on the software side, including support for additional languages and alternative theories.
Requires virtser; Allows QMK to speak the TX BOlt protocol used by stenography machines and software (such as Plover). The upside is that Plover can be configured to listen only to TX Bolt allow the keyboard to switch layers without need to enable/disable the Plover software, or to have a second non-Steno keyboard work concurrently.
This adds an action, `ACTION_SWAP_HANDS`, that swaps the the keys on the keyboard across a keymap-defined hemisphere in order to support one-hand typing without requiring a separate one-handed layer. See updated `doc/keymap.md` for more information.
