Add support for applying theme after extension is installed (#9529)

Release Notes:

- Added support for opening the theme selector with installed themes
after installing an extension containing themes.
([#9228](https://github.com/zed-industries/zed/issues/9228)).

<img width="1315" alt="Screenshot 2024-03-20 at 11 00 35 AM"
src="https://github.com/zed-industries/zed/assets/1486634/593389b3-eade-4bce-ae17-25c02a074f21">

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Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>