ARM - Initial backlight support (#6487)

* Move AVR backlight to own file, add borrowed ARM implementation

* Tiny fix for backlight custom logic

* Remove duplicate board from rebase

* Fix f303 onekey example

* clang-format

* clang-format

* Remove backlight keymap debug

* Initial pass of ARM backlight docs

* Initial pass of ARM backlight docs - resolve todos

* fix rules validation logic

* Add f072 warning

* Add f072 warning

* tidy up breathing in backlight keymap

* tidy up breathing in backlight keymap

* add missing break to backlight keymap

keyboards/handwired/onekey/keymaps/backlight/keymap.c

@@ -0,0 +1,40 @@
+#include QMK_KEYBOARD_H
+
+//Tap Dance Declarations
+enum {
+  TD_BL = 0
+};
+
+void dance_cln_finished (qk_tap_dance_state_t *state, void *user_data) {
+  // noop
+}
+
+void dance_cln_reset (qk_tap_dance_state_t *state, void *user_data) {
+  switch (state->count) {
+    case 1:
+      // single tap - step through backlight
+      backlight_step();
+      break;
+#ifdef BACKLIGHT_BREATHING
+    case 2:
+      // double tap - toggle breathing
+      breathing_toggle();
+      break;
+    case 3:
+      //tripple tap - do some pulse stuff
+      breathing_pulse();
+      break;
+#endif
+    default:
+      // more - nothing
+      break;
+  }
+}
+
+qk_tap_dance_action_t tap_dance_actions[] = {
+  [TD_BL]  = ACTION_TAP_DANCE_FN_ADVANCED (NULL, dance_cln_finished, dance_cln_reset)
+};
+
+const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
+  LAYOUT( TD(TD_BL) )
+};