Closes https://github.com/zed-industries/zed/discussions/49740

Adds optional file and folder icons to the Git panel so its file list is
easier to scan, especially in larger repositories.

- add folder icons for Git panel entries
- add Git panel settings for file and folder icon visibility

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Release Notes:

  - Made the Git Panel aware of icon themes.
  - Added the ability to render file type icons in the Git panel.

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Co-authored-by: Danilo Leal <daniloleal09@gmail.com>