fix(imgbtn) add lv_imgbtn_set_state

The normal lv_obj_add/clear_state couldn't refresh the image button properly.

docs/widgets/extra/imgbtn.md

@@ -34,6 +34,11 @@ The possible states are:
 If you set sources only in `LV_IMGBTN_STATE_RELEASED`, these sources will be used in other states too. 
 If you set e.g. `LV_IMGBTN_STATE_PRESSED` they will be used in pressed state instead of the released images.
 
+
+### States
+Instead of the regular `lv_obj_add/clear_state()` functions the `lv_imgbtn_set_state(imgbtn, LV_IMGBTN_STATE_...)` functions should be used to manually set a state.
+
+
 ## Events
 - `LV_EVENT_VALUE_CHANGED` Sent when the button is toggled.
 

src/extra/widgets/imgbtn/lv_imgbtn.c

@@ -90,6 +90,23 @@ void lv_imgbtn_set_src(lv_obj_t * obj, lv_imgbtn_state_t state, const void * src
     refr_img(obj);
 }
 
+void lv_imgbtn_set_state(lv_obj_t * obj, lv_imgbtn_state_t state)
+{
+	LV_ASSERT_OBJ(obj, MY_CLASS);
+
+	lv_state_t obj_state = LV_STATE_DEFAULT;
+	if(state == LV_IMGBTN_STATE_PRESSED || state == LV_IMGBTN_STATE_CHECKED_PRESSED) obj_state |= LV_STATE_PRESSED;
+	if(state == LV_IMGBTN_STATE_DISABLED || state == LV_IMGBTN_STATE_CHECKED_DISABLED) obj_state |= LV_STATE_DISABLED;
+	if(state == LV_IMGBTN_STATE_CHECKED_DISABLED || state == LV_IMGBTN_STATE_CHECKED_PRESSED || state == LV_IMGBTN_STATE_CHECKED_RELEASED) {
+		obj_state |= LV_STATE_CHECKED;
+	}
+
+	lv_obj_clear_state(obj, LV_STATE_CHECKED | LV_STATE_PRESSED | LV_STATE_DISABLED);
+	lv_obj_add_state(obj, obj_state);
+
+	refr_img(obj);
+}
+
 /*=====================
  * Getter functions
  *====================*/

src/extra/widgets/imgbtn/lv_imgbtn.h

@@ -78,6 +78,13 @@ void lv_imgbtn_set_src(lv_obj_t * imgbtn, lv_imgbtn_state_t state, const void *
                        const void * src_right);
 
 
+/**
+ * Use this function instead of `lv_obj_add/clear_state` to set a state manually
+ * @param imgbtn pointer to an image button object
+ * @param state  the new state
+ */
+void lv_imgbtn_set_state(lv_obj_t * imgbtn, lv_imgbtn_state_t state);
+
 /*=====================
  * Getter functions
  *====================*/