Cleanup/rgb matrix (#5811)

* clean up rgb matrix extern usage

Moved rgb matrix boiler plate into macros

Rebased onto typing heatmap pr

* Fixing the reversed frame buffer access in digital rain

* Fixing digital rain & typing heatmap if keyreactive effects are not enabled

* Apply suggestions from code review

Co-Authored-By: Drashna Jaelre <[email protected]>

* Adding parenthesizes to DRIVER_LED_TOTAL where necessary

* Updated docs

* added notes about parentheses

users/drashna/rgb_stuff.c

@@ -5,8 +5,6 @@
 #if defined(RGBLIGHT_ENABLE)
 extern rgblight_config_t rgblight_config;
 bool has_initialized;
-#elif defined(RGB_MATRIX_ENABLE)
-extern rgb_config_t rgb_matrix_config;
 #endif
 
 #ifdef RGBLIGHT_ENABLE