Allow to toggle git hunk diffs (#11080)

Part of https://github.com/zed-industries/zed/issues/4523

Added two new actions with the default keybindings

```
"cmd-'": "editor::ToggleHunkDiff",
"cmd-\"": "editor::ExpandAllHunkDiffs",
```

that allow to browse git hunk diffs in Zed:


https://github.com/zed-industries/zed/assets/2690773/9a8a7d10-ed06-4960-b4ee-fe28fc5c4768


The hunks are dynamic and alter on user folds and modifications, or
toggle hidden, if the modifications were not adjacent to the expanded
hunk.


Release Notes:

- Added `editor::ToggleHunkDiff` (`cmd-'`) and
`editor::ExpandAllHunkDiffs` (`cmd-"`) actions to browse git hunk diffs
in Zed