feat: support index arg in switch_keyboard_layout

Author: DreamMaoMao

src/config/parse_config.h

@@ -1017,6 +1017,7 @@ FuncType parse_func_name(char *func_name, Arg *arg, char *arg_value,
 		(*arg).v = strdup(arg_value);
 	} else if (strcmp(func_name, "switch_keyboard_layout") == 0) {
 		func = switch_keyboard_layout;
+		(*arg).i = CLAMP_INT(atoi(arg_value), 0, 100);
 	} else if (strcmp(func_name, "setlayout") == 0) {
 		func = setlayout;
 		(*arg).v = strdup(arg_value);

src/dispatch/bind_define.h

@@ -900,7 +900,13 @@ int32_t switch_keyboard_layout(const Arg *arg) {
 		wlr_log(WLR_INFO, "Only one layout available");
 		return 0;
 	}
-	xkb_layout_index_t next = (current + 1) % num_layouts;
+
+	xkb_layout_index_t next = 0;
+	if (arg->i > 0 && arg->i <= num_layouts) {
+		next = arg->i - 1;
+	} else {
+		next = (current + 1) % num_layouts;
+	}
 
 	// 6. 应用新 keymap
 	uint32_t depressed = keyboard->modifiers.depressed;