XR: Fix controller flicker when switching action sets

This could happen when switching between custom action sets that both
had controller pose actions. Problem was that controller data is
cleared when changing action sets, and this clearing was done when
handling WM events, which always occurs after XR controller data is
updated from GHOST.

Now, instead of activating the action set immediately, delay activation
until just before the next XR actions sync.

source/blender/makesrna/intern/rna_xr.c

@@ -849,7 +849,7 @@ bool rna_XrSessionState_active_action_set_set(bContext *C, const char *action_se
 {
 #  ifdef WITH_XR_OPENXR
   wmWindowManager *wm = CTX_wm_manager(C);
-  return WM_xr_active_action_set_set(&wm->xr, action_set_name);
+  return WM_xr_active_action_set_set(&wm->xr, action_set_name, true);
 #  else
   UNUSED_VARS(C, action_set_name);
   return false;