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

crates/editor/src/test.rs

@@ -75,3 +75,93 @@ pub(crate) fn build_editor_with_project(
 ) -> Editor {
     Editor::new(EditorMode::Full, buffer, Some(project), cx)
 }
+
+#[cfg(any(test, feature = "test-support"))]
+pub fn editor_hunks(
+    editor: &Editor,
+    snapshot: &DisplaySnapshot,
+    cx: &mut ViewContext<'_, Editor>,
+) -> Vec<(String, git::diff::DiffHunkStatus, core::ops::Range<u32>)> {
+    use text::Point;
+
+    snapshot
+        .buffer_snapshot
+        .git_diff_hunks_in_range(0..u32::MAX)
+        .map(|hunk| {
+            let display_range = Point::new(hunk.associated_range.start, 0)
+                .to_display_point(snapshot)
+                .row()
+                ..Point::new(hunk.associated_range.end, 0)
+                    .to_display_point(snapshot)
+                    .row();
+            let (_, buffer, _) = editor
+                .buffer()
+                .read(cx)
+                .excerpt_containing(Point::new(hunk.associated_range.start, 0), cx)
+                .expect("no excerpt for expanded buffer's hunk start");
+            let diff_base = &buffer
+                .read(cx)
+                .diff_base()
+                .expect("should have a diff base for expanded hunk")
+                [hunk.diff_base_byte_range.clone()];
+            (diff_base.to_owned(), hunk.status(), display_range)
+        })
+        .collect()
+}
+
+#[cfg(any(test, feature = "test-support"))]
+pub fn expanded_hunks(
+    editor: &Editor,
+    snapshot: &DisplaySnapshot,
+    cx: &mut ViewContext<'_, Editor>,
+) -> Vec<(String, git::diff::DiffHunkStatus, core::ops::Range<u32>)> {
+    editor
+        .expanded_hunks
+        .hunks(false)
+        .map(|expanded_hunk| {
+            let hunk_display_range = expanded_hunk
+                .hunk_range
+                .start
+                .to_display_point(snapshot)
+                .row()
+                ..expanded_hunk
+                    .hunk_range
+                    .end
+                    .to_display_point(snapshot)
+                    .row();
+            let (_, buffer, _) = editor
+                .buffer()
+                .read(cx)
+                .excerpt_containing(expanded_hunk.hunk_range.start, cx)
+                .expect("no excerpt for expanded buffer's hunk start");
+            let diff_base = &buffer
+                .read(cx)
+                .diff_base()
+                .expect("should have a diff base for expanded hunk")
+                [expanded_hunk.diff_base_byte_range.clone()];
+            (
+                diff_base.to_owned(),
+                expanded_hunk.status,
+                hunk_display_range,
+            )
+        })
+        .collect()
+}
+
+#[cfg(any(test, feature = "test-support"))]
+pub fn expanded_hunks_background_highlights(
+    editor: &Editor,
+    snapshot: &DisplaySnapshot,
+) -> Vec<core::ops::Range<u32>> {
+    use itertools::Itertools;
+
+    editor
+        .highlighted_rows::<crate::DiffRowHighlight>()
+        .into_iter()
+        .flatten()
+        .map(|(range, _)| {
+            range.start.to_display_point(snapshot).row()..range.end.to_display_point(snapshot).row()
+        })
+        .unique()
+        .collect()
+}