git: Make permalinks aware of current diffs (#41915)

Addressing #22546, we want git permalinks to be aware of the current
changes within the buffer.

This change calculates how many lines have been added/deleted between
the start and end of the selection and uses those values to offset the
selection.

This is done within `Editor::get_permalink_to_line` so that it can be
passed to any git_store.

Example:

<img width="284" height="316" alt="image"
src="https://github.com/user-attachments/assets/268043a0-2fc8-41c1-b094-d650fd4e0ae0"
/>

Where this selections permalink would previously return L3-L9, it now
returns L2-L7.

Release Notes:

- git: make permalinks aware of current diffs

Closes #22546

---

This is my first PR into the zed repository so very happy for any
feedback on how I've implemented this. Thanks!

crates/editor/src/editor.rs

@@ -20973,9 +20973,22 @@ impl Editor {
                 buffer_ranges.last()
             }?;
 
-            let selection = text::ToPoint::to_point(&range.start, buffer).row
-                ..text::ToPoint::to_point(&range.end, buffer).row;
-            Some((multi_buffer.buffer(buffer.remote_id()).unwrap(), selection))
+            let start_row_in_buffer = text::ToPoint::to_point(&range.start, buffer).row;
+            let end_row_in_buffer = text::ToPoint::to_point(&range.end, buffer).row;
+
+            let Some(buffer_diff) = multi_buffer.diff_for(buffer.remote_id()) else {
+                let selection = start_row_in_buffer..end_row_in_buffer;
+
+                return Some((multi_buffer.buffer(buffer.remote_id()).unwrap(), selection));
+            };
+
+            let buffer_diff_snapshot = buffer_diff.read(cx).snapshot(cx);
+
+            Some((
+                multi_buffer.buffer(buffer.remote_id()).unwrap(),
+                buffer_diff_snapshot.row_to_base_text_row(start_row_in_buffer, buffer)
+                    ..buffer_diff_snapshot.row_to_base_text_row(end_row_in_buffer, buffer),
+            ))
         });
 
         let Some((buffer, selection)) = buffer_and_selection else {