[Core] Tri Layer Keys (#19795)

Co-authored-by: wilba <[email protected]>
Co-authored-by: Pablo Martínez <[email protected]>
Co-authored-by: Joel Challis <[email protected]>
Co-authored-by: Nick Brassel <[email protected]>

quantum/action_layer.c

@@ -349,3 +349,13 @@ uint8_t layer_switch_get_layer(keypos_t key) {
 action_t layer_switch_get_action(keypos_t key) {
     return action_for_key(layer_switch_get_layer(key), key);
 }
+
+layer_state_t update_tri_layer_state(layer_state_t state, uint8_t layer1, uint8_t layer2, uint8_t layer3) {
+    layer_state_t mask12 = ((layer_state_t)1 << layer1) | ((layer_state_t)1 << layer2);
+    layer_state_t mask3  = (layer_state_t)1 << layer3;
+    return (state & mask12) == mask12 ? (state | mask3) : (state & ~mask3);
+}
+
+void update_tri_layer(uint8_t layer1, uint8_t layer2, uint8_t layer3) {
+    layer_state_set(update_tri_layer_state(layer_state, layer1, layer2, layer3));
+}