[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/tri_layer.c

@@ -0,0 +1,39 @@
+// Copyright 2023 QMK
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include "tri_layer.h"
+#include <stdint.h>
+
+static uint8_t tri_layer_lower_layer  = TRI_LAYER_LOWER_LAYER;
+static uint8_t tri_layer_upper_layer  = TRI_LAYER_UPPER_LAYER;
+static uint8_t tri_layer_adjust_layer = TRI_LAYER_ADJUST_LAYER;
+
+void set_tri_layer_lower_layer(uint8_t layer) {
+    tri_layer_lower_layer = layer;
+}
+
+void set_tri_layer_upper_layer(uint8_t layer) {
+    tri_layer_upper_layer = layer;
+}
+
+void set_tri_layer_adjust_layer(uint8_t layer) {
+    tri_layer_adjust_layer = layer;
+}
+
+void set_tri_layer_layers(uint8_t lower, uint8_t raise, uint8_t adjust) {
+    tri_layer_lower_layer  = lower;
+    tri_layer_upper_layer  = raise;
+    tri_layer_adjust_layer = adjust;
+}
+
+uint8_t get_tri_layer_lower_layer(void) {
+    return tri_layer_lower_layer;
+}
+
+uint8_t get_tri_layer_upper_layer(void) {
+    return tri_layer_upper_layer;
+}
+
+uint8_t get_tri_layer_adjust_layer(void) {
+    return tri_layer_adjust_layer;
+}