fix(style) rename path_cb to to path_xcb in lv_style_transition_dsc_t

This way the MicroPython won't allow manually setting this field.
And it can't be set manually becasue the user data needs to be set too.
So lv_style_transition_dsc_init() should be used to initialize the fields of lv_style_transition_dsc_t

src/core/lv_obj.c

@@ -1009,7 +1009,7 @@ static void lv_obj_set_state(lv_obj_t * obj, lv_state_t new_state)
             if(t == tsi) {
                 ts[tsi].time = tr->time;
                 ts[tsi].delay = tr->delay;
-                ts[tsi].path_cb = tr->path_cb;
+                ts[tsi].path_cb = tr->path_xcb;
                 ts[tsi].prop = tr->props[j];
 #if LV_USE_USER_DATA
                 ts[tsi].user_data = tr->user_data;

src/misc/lv_style.c

@@ -202,7 +202,7 @@ void lv_style_transition_dsc_init(lv_style_transition_dsc_t * tr, const lv_style
 {
     lv_memset_00(tr, sizeof(lv_style_transition_dsc_t));
     tr->props = props;
-    tr->path_cb = path_cb == NULL ? lv_anim_path_linear : path_cb;
+    tr->path_xcb = path_cb == NULL ? lv_anim_path_linear : path_cb;
     tr->time = time;
     tr->delay = delay;
 }

src/misc/lv_style.h

@@ -231,7 +231,7 @@ typedef struct _lv_style_transiton_t {
 #if LV_USE_USER_DATA
     void * user_data;              /**< A custom user data that will be passed to the animation's user_data */
 #endif
-    lv_anim_path_cb_t path_cb;     /**< A path for the animation.*/
+    lv_anim_path_cb_t path_xcb;     /**< A path for the animation.*/
     uint32_t time;                 /**< Duration of the transition in [ms]*/
     uint32_t delay;                /**< Delay before the transition in [ms]*/
 }lv_style_transition_dsc_t;