Implement staging and unstaging hunks (#24606)

- [x] Staging hunks
- [x] Unstaging hunks
- [x] Write a randomized test
- [x] Get test passing
- [x] Fix existing bug in diff_base_byte_range computation
- [x] Remote project support
- [ ] ~~Improve performance of
buffer_range_to_unchanged_diff_base_range~~
- [ ] ~~Bug: project diff editor scrolls to top when staging/unstaging
hunk~~ existing issue
- [ ] ~~UI~~ deferred
- [x] Tricky cases
  - [x] Correctly handle acting on multiple hunks for a single file
- [x] Remove path from index when unstaging the last staged hunk, if
it's absent from HEAD, or staging the only hunk, if it's deleted in the
working copy

Release Notes:

- Add `ToggleStagedSelectedDiffHunks` action for staging and unstaging
individual diff hunks

crates/buffer_diff/Cargo.toml

@@ -20,14 +20,18 @@ futures.workspace = true
 git2.workspace = true
 gpui.workspace = true
 language.workspace = true
+log.workspace = true
 rope.workspace = true
 sum_tree.workspace = true
 text.workspace = true
 util.workspace = true
 
 [dev-dependencies]
+ctor.workspace = true
+env_logger.workspace = true
+gpui = { workspace = true, features = ["test-support"] }
 pretty_assertions.workspace = true
+rand.workspace = true
 serde_json.workspace = true
 text = { workspace = true, features = ["test-support"] }
-gpui = { workspace = true, features = ["test-support"] }
 unindent.workspace = true