Rework mouse handling of git hunks diff (#14727)

Closes https://github.com/zed-industries/zed/issues/12404

![Screenshot 2024-07-18 at 14 02
31](https://github.com/user-attachments/assets/a8addd22-0ed9-4f4b-852a-f347314c27ce)

![Screenshot 2024-07-18 at 14 02
43](https://github.com/user-attachments/assets/0daaed10-b9f3-4d4b-b8d7-189aa7e013b9)

Video:


https://github.com/user-attachments/assets/58e62527-da75-4017-a43e-a37803bd7b49


* now shows a context menu on left click instead of expanding the hunk
diff
* hunk diffs can be toggled with a single cmd-click still
* adds a X mark into gutter for every hunk expanded
* makes `editor::ToggleDiffHunk` to work inside the deleted hunk editors

Additionally, changes the way editor context menus behave when the
editor is scrolled — right click and diff hunks context menu now will
stick to the place it was invoked at, instead of staying onscreen at the
same pixel positions.

Release Notes:

- Improved the way git hunks diff can be toggled with mouse
([#12404](https://github.com/zed-industries/zed/issues/12404))

---------

Co-authored-by: Nate Butler <nate@zed.dev>
Co-authored-by: Conrad Irwin <conrad@zed.dev>

crates/diagnostics/src/grouped_diagnostics.rs

@@ -319,7 +319,7 @@ impl GroupedDiagnosticsEditor {
                 || server_to_update.map_or(false, |to_update| *server_id != to_update)
         });
 
-        // TODO kb change selections as in the old panel, to the next primary diagnostics
+        // TODO change selections as in the old panel, to the next primary diagnostics
         // TODO make [shift-]f8 to work, jump to the next block group
         let _was_empty = self.path_states.is_empty();
         let path_ix = match self.path_states.binary_search_by(|probe| {