tab_switcher: Use git-aware colors for file icons (#18733)

Release Notes:

- Fixed tab switcher icons not respecting the `tabs.git_status` setting.

Fixes an issue mentioned in
https://github.com/zed-industries/zed/pull/17115#issuecomment-2378966170
- file icons in the tab switcher weren't colored according to git
status, even if `tabs.git_status` was set to true.

I used a similar approach I saw in other places of the project to get
the project entry and its git status, but maybe we could move the
coloring logic entirely to `tab_icon()`? Wouldn't this break anything?

---------

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

Cargo.lock

@@ -11412,6 +11412,7 @@ dependencies = [
  "project",
  "serde",
  "serde_json",
+ "settings",
  "theme",
  "ui",
  "util",