Add progress bar to "Downloading Zed Update..." button (#60294)

# Objective

On a few occasions I have been wondering if the Zed update download had
stalled, when in fact it's just taking a while. This PR adds a progress
bar to the "Downloading Zed Update..." button to give users feedback
that the download is indeed progressing.

## Solution

Add a custom progress bar inside the button. I tried reusing the
existing ProgressBar component but that has a fixed height of 8px which
caused the button to become taller.

## Testing

- Tested manually using the command palette `collab: simulate update
available` and stepping through the different UI states.
- Added unit test

## Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content adheres to Zed's UI standards
([UX/UI](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
and
[icon](https://github.com/zed-industries/zed/blob/main/crates/icons/README.md)
guidelines)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

## Showcase

<img width="1350" height="748" alt="Image 02-07-2026 at 17 23"
src="https://github.com/user-attachments/assets/ed23c97a-01b8-446b-9693-0c53a69b419d"
/>

Release Notes:

- Added a download progress indicator to the update button.

---------

Co-authored-by: Smit Barmase <heysmitbarmase@gmail.com>
4a3b763518Chiel Robben committed on 7/3/2026, 8:23:06 AM· committed by GitHubparentf961889
4 files changedLine totals unavailable