Show type-changed files in commit diffs (#60422)

# Objective

Zed ignores files marked by Git as type-changed (T), causing commits
containing only these changes to show 0 Changed Files.

For example, commit d7cc949e61351a6028f933abbaea39f67af9dfb2 changes
crates/eval_utils/LICENSE-GPL from a regular file to a symlink, but Zed
displays no changes.

  ## Solution

Handle TypeChanged files like modified files by loading both their old
and new contents.

  ## Testing

  - Added parser coverage for the T status.
  - Added a repository test for a regular-file-to-symlink change.
  - Ran cargo test -p git.
  - Ran ./script/clippy -p git.
  - Manually verified the example commit on macOS.

  ## 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

Before:
<img width="200" alt="image"
src="https://github.com/user-attachments/assets/277c5938-5c2c-47b7-902d-9061a14c062a"
/>

After:
<img width="200" alt="image"
src="https://github.com/user-attachments/assets/f99d0005-0712-4843-814e-d73b11f64782"
/>

  ———

  Release Notes:

- Fixed type-changed files not appearing in Git Graph and commit views.

crates/git/src/commit.rs

@@ -109,6 +109,7 @@ pub fn parse_git_diff_name_status(content: &str) -> impl Iterator<Item = (&str,
             let path = parts.next()?;
             let status = match status_str {
                 "M" => StatusCode::Modified,
+                "T" => StatusCode::TypeChanged,
                 "A" => StatusCode::Added,
                 "D" => StatusCode::Deleted,
                 _ => continue,
@@ -127,6 +128,7 @@ mod tests {
     fn test_parse_git_diff_name_status() {
         let input = concat!(
             "M\x00Cargo.lock\x00",
+            "T\x00LICENSE-GPL\x00",
             "M\x00crates/project/Cargo.toml\x00",
             "M\x00crates/project/src/buffer_store.rs\x00",
             "D\x00crates/project/src/git.rs\x00",
@@ -142,6 +144,7 @@ mod tests {
             output,
             &[
                 ("Cargo.lock", StatusCode::Modified),
+                ("LICENSE-GPL", StatusCode::TypeChanged),
                 ("crates/project/Cargo.toml", StatusCode::Modified),
                 ("crates/project/src/buffer_store.rs", StatusCode::Modified),
                 ("crates/project/src/git.rs", StatusCode::Deleted),