[Core] Tri Layer Keys (#19795)

Co-authored-by: wilba <wilba@wilba.tech>
Co-authored-by: Pablo Martínez <58857054+elpekenin@users.noreply.github.com>
Co-authored-by: Joel Challis <git@zvecr.com>
Co-authored-by: Nick Brassel <nick@tzarc.org>

quantum/quantum.h

@@ -240,9 +240,10 @@ extern layer_state_t layer_state;
 #    include "process_autocorrect.h"
 #endif
 
-// For tri-layer
-void          update_tri_layer(uint8_t layer1, uint8_t layer2, uint8_t layer3);
-layer_state_t update_tri_layer_state(layer_state_t state, uint8_t layer1, uint8_t layer2, uint8_t layer3);
+#ifdef TRI_LAYER_ENABLE
+#    include "tri_layer.h"
+#    include "process_tri_layer.h"
+#endif
 
 void set_single_persistent_default_layer(uint8_t default_layer);