Refactor quantum/command.{c,h} for code size & {read,maintain}abili…

…ty (#11842)

* quantum/command.c: coalesce `print()`s in `command_common_help()` & `print_version()`

Also undo some damage by clang-format in b624f32

* quantum/command.c: replace `print(…); print_{,val_}{dec,hex}*(…);` sequences with single `xprintf(…)`

`print_{dec,hex}*(…)` are just `#define`s for `xprintf(…)` anyway.

Each additional `xprintf(…)` costs ~8 bytes: the call instructions,
plus an additional NUL terminator.

This _really_ adds up: this commit saves 814 bytes on my ATmega32.

* quantum/command.c: optimise `mousekey_console()` for size & legibility

Made various tweaks to the interface, but still functionally identical.

Assume `KC_1`…`KC_0` to be contiguous, and removed `numkey2num(…)` entirely.
It was exported in `command.h` by 1a0bac8 for no obvious reason, before
which it was `static`. I doubt anyone uses it.

`mousekey_console()` is now enabled regardless of `MK_3_SPEED`.
Needs fleshing out for things other than the X11 variant though.

This commit saves 638 bytes on my ATmega32.