vim: Add motion support for toggle comments (#14919)

### Summary

This PR adds support for count and object motions to the toggle comments
action in Vim mode. The relevant issue is
[#14337](https://github.com/zed-industries/zed/issues/14337).

For example, `2 g c j` will toggle comments three lines downward. `g c g
g` will toggle comments from the current cursor position up to the start
of the file.

Notably missing from this PR are `g c b` (toggle comments for the
current block) as well as `g c p` (toggle comments for the current
paragraph). These seem to be non-standard.

The new module `normal/toggle_comments.rs` has been copied almost
verbatim from `normal/indent.rs`. Maybe that ought to be abstracted over
but I feel I lack the overview.

Release Notes:

- vim: Added support for count and object motion to the toggle comments
action ([#14337](https://github.com/zed-industries/zed/issues/14337)).

crates/vim/src/test.rs

@@ -1268,6 +1268,29 @@ async fn test_toggle_comments(cx: &mut gpui::TestAppContext) {
           "},
         Mode::Normal,
     );
+
+    // works with count
+    cx.simulate_keystrokes("g c 2 j");
+    cx.assert_state(
+        indoc! {"
+            // // ˇone
+            // two
+            // three
+            "},
+        Mode::Normal,
+    );
+
+    // works with motion object
+    cx.simulate_keystrokes("shift-g");
+    cx.simulate_keystrokes("g c g g");
+    cx.assert_state(
+        indoc! {"
+            // one
+            two
+            three
+            ˇ"},
+        Mode::Normal,
+    );
 }
 
 #[gpui::test]