git_ui: New panel design (#25821)

This PR updates the ui of the git panel. It removes the header from the
panel and unifies the repository, branch and commit controls in the
bottom section.

It also adds a secondary menu to the primary button giving access to a
variety of actions for managing local and remote changes:

![CleanShot 2025-02-28 at 12 18
15@2x](https://github.com/user-attachments/assets/0260c122-405f-46fc-8cc8-d6beac782b9d)

Known issues (will be fixed in a later pr)
- Spinner showing git operation progress was removed, will be re-added
- Clicking expand with the panel editor focused will commit (due to
shared action name. Already tracked)

Before | After

![CleanShot 2025-02-28 at 12 22
18@2x](https://github.com/user-attachments/assets/4c1e4ac9-b975-487f-bf4e-8815a8da4f4f)

(Also adds `component`, `linkme` to cargo-machete ignore as they are
used in the `IntoComponent` proc-macro and will always be incorrectly
flagged as unused)

Release Notes:

- N/A

---------

Co-authored-by: Cole Miller <m@cole-miller.net>
Co-authored-by: Cole Miller <53574922+cole-miller@users.noreply.github.com>
Co-authored-by: Cole Miller <cole@zed.dev>

Cargo.lock

@@ -5395,6 +5395,7 @@ dependencies = [
  "anyhow",
  "buffer_diff",
  "collections",
+ "component",
  "db",
  "editor",
  "feature_flags",
@@ -5404,6 +5405,7 @@ dependencies = [
  "gpui",
  "itertools 0.14.0",
  "language",
+ "linkme",
  "menu",
  "multi_buffer",
  "panel",
@@ -5415,6 +5417,7 @@ dependencies = [
  "serde_derive",
  "serde_json",
  "settings",
+ "smallvec",
  "strum",
  "theme",
  "time",