Discussed in zed-industries#6668 specifically this comment from @zackangelo:

> The biggest thing keeping me from using Zed as a daily driver is error
indication in the project panel. When I'm making big project-wide
changes I can't clearly see which files have errors (in editors like
VSCode the filenames turn red).

> VSCode seems to use a letter on the right gutter to indicate git
status and a number next to it to indicate diagnostic status. The color
indicates either.

This PR implements that, I added an opt-in `diagnostic_badges` setting
(default is false) that shows error and warning counts as colored labels
on the right side of each project panel entry. Counts bubble up to
parent directories.

When `diagnostic_badges` is enabled, diagnostic severity takes priority
over git status for entry text color.
Since warnings and git-modified share the same yellow, git status with
this option on is readable through the file icon decoration and the
absence of a number badge on the right.

Example:
<img width="522" height="785" alt="image"
src="https://github.com/user-attachments/assets/2da62580-86fe-480b-9b57-ff137ea42285"
/>


<img width="884" height="580" alt="image"
src="https://github.com/user-attachments/assets/198e9a45-dacd-4f1e-a66c-f2b84fd4db63"
/>

Release Notes:
- Added diagnostic count badges to the project panel, displaying error
and warning counts next to file names. You can modify this setting using
the `diagnostic_badges` option, which is enabled by default.

---------

Co-authored-by: Smit Barmase <[email protected]>

This PR adds Git status badges next to file names in the Project Panel,
following my older PR #49802
These are enabled by having "git_status" true.

Screenshot
<img width="343" height="320" alt="image"
src="https://github.com/user-attachments/assets/b2c208bf-5027-4947-a5ee-eeb74fadb02b"
/>

I'd love to hear feedback about any of this :)
Especially feedback on these:

- File name colour is determined only by Git status, the diagnostic
badges remain separate. Should diagnostics also affect the filename
colour?
- (Unstaged) Modified files and staged modifications share the same
colour, in vscode staged modifications use a brownish colour by default
which I could not find the colours. I think differentiating them is
definetely something to add.

Release Notes

- Added git status indicators in Project Panel. It can be enabled by
setting `git_status_indicator` to `true` in `project_panel` settings.

---------

Co-authored-by: Smit Barmase <[email protected]>