Fix two mouse event bugs (#2835)

This PR fixes two bugs we discovered in Zed's mouse event handling while
investigating an interesting and mysterious bug we we were seeing, where
spurious `MouseMoved` events would continuously be dispatched after
control-clicking.

Release Notes:

- Fixed a rendering glitch that could occur after control-clicking
certain elements.

crates/gpui/src/platform/mac/window.rs

@@ -1087,7 +1087,10 @@ extern "C" fn handle_view_event(this: &Object, _: Sel, native_event: id) {
                 button: MouseButton::Left,
                 modifiers: Modifiers { ctrl: true, .. },
                 ..
-            }) => return,
+            }) => {
+                window_state_borrow.synthetic_drag_counter += 1;
+                return;
+            }
 
             _ => None,
         };