Event System: use more thoroughly tested logic for click-drag events

No functional changes, largely restoring old logic & removing the need
for workarounds.

Reverts:
- 13b6cec039.
- aa71414dfc (partially).

source/blender/windowmanager/intern/wm_event_system.c

@@ -3191,11 +3191,15 @@ static int wm_handlers_do(bContext *C, wmEvent *event, ListBase *handlers)
           copy_v2_v2_int(event->xy, prev_xy);
 
           win->event_queue_check_click = false;
+          if (!((action & WM_HANDLER_BREAK) == 0 || wm_action_not_handled(action))) {
+            /* Only disable when handled as other handlers may use this drag event. */
+            win->event_queue_check_drag = false;
+          }
         }
       }
-      else {
-        win->event_queue_check_drag = false;
-      }
+    }
+    else {
+      win->event_queue_check_drag = false;
     }
   }
   else if (ISMOUSE_BUTTON(event->type) || ISKEYBOARD(event->type)) {
@@ -3267,6 +3271,7 @@ static int wm_handlers_do(bContext *C, wmEvent *event, ListBase *handlers)
     }
     else {
       win->event_queue_check_click = false;
+      win->event_queue_check_drag = false;
     }
   }
   else if (ISMOUSE_WHEEL(event->type) || ISMOUSE_GESTURE(event->type)) {
@@ -3713,11 +3718,6 @@ void wm_event_do_handlers(bContext *C)
       /* Check dragging, creates new event or frees, adds draw tag. */
       wm_event_drag_and_drop_test(wm, win, event);
 
-      /* Builtin drag: #KM_CLICK_DRAG. */
-      if (action & WM_HANDLER_BREAK) {
-        win->event_queue_check_drag = false;
-      }
-
       if ((action & WM_HANDLER_BREAK) == 0) {
         /* NOTE: setting subwin active should be done here, after modal handlers have been done. */
         if (event->type == MOUSEMOVE) {

source/blender/windowmanager/intern/wm_gesture_ops.c

@@ -162,13 +162,6 @@ static bool gesture_box_apply(bContext *C, wmOperator *op)
 
 int WM_gesture_box_invoke(bContext *C, wmOperator *op, const wmEvent *event)
 {
-  /* FIXME(@campbellbarton): This is a temporary workaround T96120. As events
-   * are handled while dragging we should resolve this in a more general way. */
-  wmWindowManager *wm = CTX_wm_manager(C);
-  if (wm->drags.first) {
-    return OPERATOR_PASS_THROUGH;
-  }
-
   wmWindow *win = CTX_wm_window(C);
   const ARegion *region = CTX_wm_region(C);
   const bool wait_for_input = !WM_event_is_mouse_drag_or_press(event) &&