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">

---------

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

Cargo.lock

@@ -3528,6 +3528,7 @@ dependencies = [
  "settings",
  "smallvec",
  "theme",
+ "theme_selector",
  "ui",
  "util",
  "workspace",
@@ -9619,6 +9620,7 @@ dependencies = [
  "gpui",
  "log",
  "picker",
+ "serde",
  "settings",
  "theme",
  "ui",