backlight breathing overhaul (#2187)

* add breathing to bananasplit

* backlight breathing overhaul

* fix the backlight_tick thing.

* fix for vision_division backlight

* fix a few keymaps and probably break breathing for some weirdly set-up boards.

* remove BL_x keycodes because they made unreasonable assumptions

* some fixes for BL keycodes

* integer cie lightness scaling

* use cie lightness for non-breathing backlight and make breathing able to reach true max brightness

quantum/quantum_keycodes.h

@@ -380,26 +380,13 @@ enum quantum_keycodes {
 #endif // MIDI_ADVANCED
 
     // Backlight functionality
-    BL_0,
-    BL_1,
-    BL_2,
-    BL_3,
-    BL_4,
-    BL_5,
-    BL_6,
-    BL_7,
-    BL_8,
-    BL_9,
-    BL_10,
-    BL_11,
-    BL_12,
-    BL_13,
-    BL_14,
-    BL_15,
+    BL_ON,
+    BL_OFF,
     BL_DEC,
     BL_INC,
     BL_TOGG,
     BL_STEP,
+    BL_BRTG,
 
     // RGB functionality
     RGB_TOG,
@@ -579,9 +566,6 @@ enum quantum_keycodes {
 #define AG_SWAP MAGIC_SWAP_ALT_GUI
 #define AG_NORM MAGIC_UNSWAP_ALT_GUI
 
-#define BL_ON  BL_9
-#define BL_OFF BL_0
-
 // GOTO layer - 16 layers max
 // when:
 // ON_PRESS    = 1