Fix Gallery preview_close event not firing on ESC key (#12577)
* Fix Gallery preview_close event not firing on ESC key (#12553)
The on_keydown handler was setting selected_index to null when ESC
was pressed, but it wasn't dispatching the preview_close event.
The close button (X) correctly dispatches this event, so ESC key
should have the same behavior.
Changes:
- Add dispatch("preview_close") in on_keydown when Escape is pressed
- Add test case for ESC key triggering preview_close event
* add changeset
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