Follow up: https://github.com/zed-industries/zed/pull/55167,
https://github.com/zed-industries/zed/pull/54468

This is the final PR for adding remote support on the git graph. It uses
the client stream request support added in #55167 to add support for the
initial graph data request. I also fixed a bug where
`GitGraph::FullyLoaded` repository event was never emitted.

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 is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [ ] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Closes ##53040

Co-authored-by: Remco Smits \<djsmits12@gmail.com\>

Release Notes:

- git_graph: Add remote support

---------

Co-authored-by: Ben Kunkle <ben@zed.dev>