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

assets/settings/default.json

@@ -299,7 +299,9 @@
   // The list of language servers to use (or disable) for all languages.
   //
   // This is typically customized on a per-language basis.
-  "language_servers": ["..."],
+  "language_servers": [
+    "..."
+  ],
   // When to automatically save edited buffers. This setting can
   // take four values.
   //
@@ -428,7 +430,9 @@
   "copilot": {
     // The set of glob patterns for which copilot should be disabled
     // in any matching file.
-    "disabled_globs": [".env"]
+    "disabled_globs": [
+      ".env"
+    ]
   },
   // Settings specific to journaling
   "journal": {
@@ -539,7 +543,12 @@
         // Default directories to search for virtual environments, relative
         // to the current working directory. We recommend overriding this
         // in your project's settings, rather than globally.
-        "directories": [".env", "env", ".venv", "venv"],
+        "directories": [
+          ".env",
+          "env",
+          ".venv",
+          "venv"
+        ],
         // Can also be 'csh', 'fish', and `nushell`
         "activate_script": "default"
       }