Fix snap gizmo flickering while dragging

Ignore click-drag for non-mouse button drag events

Alternative to fix issue detailed in D10886.

source/blender/windowmanager/WM_api.h

@@ -861,6 +861,7 @@ int WM_event_modifier_flag(const struct wmEvent *event);
 
 bool WM_event_is_modal_tweak_exit(const struct wmEvent *event, int tweak_event);
 bool WM_event_is_last_mousemove(const struct wmEvent *event);
+bool WM_event_is_mouse_drag(const struct wmEvent *event);
 
 int WM_event_drag_threshold(const struct wmEvent *event);
 bool WM_event_drag_test(const struct wmEvent *event, const int prev_xy[2]);

source/blender/windowmanager/gizmo/intern/wm_gizmo_group.c

@@ -592,7 +592,7 @@ static int gizmo_tweak_invoke(bContext *C, wmOperator *op, const wmEvent *event)
   const int highlight_part_init = gz->highlight_part;
 
   if (gz->drag_part != -1) {
-    if (ISTWEAK(event->type) || (event->val == KM_CLICK_DRAG)) {
+    if (WM_event_is_mouse_drag(event)) {
       gz->highlight_part = gz->drag_part;
     }
   }

source/blender/windowmanager/gizmo/intern/wm_gizmo_map.c

@@ -735,7 +735,7 @@ wmGizmo *wm_gizmomap_highlight_find(wmGizmoMap *gzmap,
 
   /* Ensure for drag events we use the location where the user clicked.
    * Without this click-dragging on a gizmo can accidentally act on the wrong gizmo. */
-  if (ISTWEAK(event->type) || (event->val == KM_CLICK_DRAG)) {
+  if (WM_event_is_mouse_drag(event)) {
     mval[0] += event->x - event->prevclickx;
     mval[1] += event->y - event->prevclicky;
   }

source/blender/windowmanager/intern/wm_event_query.c

@@ -265,6 +265,11 @@ bool WM_event_is_last_mousemove(const wmEvent *event)
   return true;
 }
 
+bool WM_event_is_mouse_drag(const wmEvent *event)
+{
+  return ISTWEAK(event->type) || (ISMOUSE_BUTTON(event->type) && (event->val == KM_CLICK_DRAG));
+}
+
 /** \} */
 
 /* -------------------------------------------------------------------- */