git_ui: Fix open diff for untracked files when sorting by path enabled (#39862)

Fixes the `Open Diff` action for untracked files when the `sort_by_path`
setting is enabled. The `ProjectDiff` wasn't correctly moving the
multibuffer's cursor to the untracked file because, when that setting is
enabled, it's sort prefix is changed to the tracked files sort prefix, and that
wasn't accounted for in `move_to_entry`.

Before these changes, the `sort_prefix` field for `PathKey` was called `namespace`, it was renamed to be clearer what its purpose is.

Closes #39529 

Release Notes:

- Fixed 'Open Diff' action for untracked files when `sort_by_path` is
enabled

---------

Co-authored-by: David Kleingeld <davidsk@zed.dev>

crates/git_ui/src/commit_view.rs

@@ -43,8 +43,8 @@ struct CommitMetadataFile {
     worktree_id: WorktreeId,
 }
 
-const COMMIT_METADATA_NAMESPACE: u64 = 0;
-const FILE_NAMESPACE: u64 = 1;
+const COMMIT_METADATA_SORT_PREFIX: u64 = 0;
+const FILE_NAMESPACE_SORT_PREFIX: u64 = 1;
 
 impl CommitView {
     pub fn open(
@@ -145,7 +145,7 @@ impl CommitView {
             });
             multibuffer.update(cx, |multibuffer, cx| {
                 multibuffer.set_excerpts_for_path(
-                    PathKey::namespaced(COMMIT_METADATA_NAMESPACE, file.title.clone()),
+                    PathKey::with_sort_prefix(COMMIT_METADATA_SORT_PREFIX, file.title.clone()),
                     buffer.clone(),
                     vec![Point::zero()..buffer.read(cx).max_point()],
                     0,
@@ -193,7 +193,7 @@ impl CommitView {
                             .collect::<Vec<_>>();
                         let path = snapshot.file().unwrap().path().clone();
                         let _is_newly_added = multibuffer.set_excerpts_for_path(
-                            PathKey::namespaced(FILE_NAMESPACE, path),
+                            PathKey::with_sort_prefix(FILE_NAMESPACE_SORT_PREFIX, path),
                             buffer,
                             diff_hunk_ranges,
                             multibuffer_context_lines(cx),