Add checkbox to only show installed extensions (#8208)

This PR adds a checkbox to the extensions view to allow filtering to
just extensions that are installed:

<img width="1408" alt="Screenshot 2024-02-22 at 12 05 40 PM"
src="https://github.com/zed-industries/zed/assets/1486634/b5e82941-53be-432e-bfe5-fec7fd0959c5">

Release Notes:

- Added a checkbox to the extensions view to only show installed
extensions.
af06063d31Marshall Bowers committed on 2/22/2024, 5:16:02 PM· committed by GitHubparent5c4f3c0
2 files changedLine totals unavailable