feat(keymap): Add binding get/set, layer movement

* Add keymap API for getting/setting a bindings
  in keymap layers.
* Add layer move support via intemediary ordering array.
* Add settings storage for keymap changes.

app/Kconfig

@@ -258,6 +258,18 @@ rsource "src/split/Kconfig"
 #Basic Keyboard Setup
 endmenu
 
+menu "Keymaps"
+
+config ZMK_KEYMAP_LAYER_REORDERING
+    bool "Layer Reordering Support"
+
+config ZMK_KEYMAP_SETTINGS_STORAGE
+    bool "Settings Save/Load"
+    depends on SETTINGS
+    depends on ZMK_BEHAVIOR_LOCAL_IDS
+
+endmenu # Keymaps
+
 rsource "src/studio/Kconfig"
 
 menu "Display/LED Options"

app/include/zmk/keymap.h

@@ -24,6 +24,28 @@ int zmk_keymap_layer_toggle(uint8_t layer);
 int zmk_keymap_layer_to(uint8_t layer);
 const char *zmk_keymap_layer_name(uint8_t layer);
 
+const struct zmk_behavior_binding *zmk_keymap_get_layer_binding_at_idx(uint8_t layer,
+                                                                       uint8_t binding_idx);
+int zmk_keymap_set_layer_binding_at_idx(uint8_t layer, uint8_t binding_idx,
+                                        const struct zmk_behavior_binding binding);
+
+#if IS_ENABLED(CONFIG_ZMK_KEYMAP_LAYER_REORDERING)
+
+int zmk_keymap_move_layer(uint8_t layer, uint8_t dest);
+
+#endif
+
+/**
+ * @brief Check if there are any unsaved keymap changes.
+ *
+ * @retval 0 if there are no changes.
+ * @retval 1 if there are changes.
+ */
+int zmk_keymap_check_unsaved_changes(void);
+
+int zmk_keymap_save_changes(void);
+int zmk_keymap_discard_changes(void);
+
 int zmk_keymap_position_state_changed(uint8_t source, uint32_t position, bool pressed,
                                       int64_t timestamp);