Add shift-to-invert to remaining directional RGB_* keycode pairs (#7484)

Add shift-to-invert to remaining directional RGB_* keycode pairs (#7484)

* Add shift-to-invert to remaining directional RGB_* keycode pairs

RGB_MODE_FORWARD / RGB_MODE_REVERSE invert their functions when shift is held.
This change adds the same capabilities to the remaining directional RGB_*
keycode pairs.  This improves consistency and provides full RGB control in a
keymap containing only one keycode from each pair.

* remove redundant variable

* fix typo

* Fix more typos

Flyspell is on now I swear!