Fixes https://github.com/zed-industries/zed/issues/9300

This was a regression caused by not inserting a hitbox when a div only
had click listeners on it.

Release Notes:

- Fixed a regression that disabled double-clicking on the titlebar to
zoom the window.
([#9300](https://github.com/zed-industries/zed/issues/9300))
(preview-only)