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/state.rs

@@ -71,6 +71,7 @@ pub enum Operator {
     Register,
     RecordRegister,
     ReplayRegister,
+    ToggleComments,
 }
 
 #[derive(Default, Clone)]
@@ -326,6 +327,7 @@ impl Operator {
             Operator::Register => "\"",
             Operator::RecordRegister => "q",
             Operator::ReplayRegister => "@",
+            Operator::ToggleComments => "gc",
         }
     }
 
@@ -351,7 +353,8 @@ impl Operator {
             | Operator::Uppercase
             | Operator::Object { .. }
             | Operator::ChangeSurrounds { target: None }
-            | Operator::OppositeCase => false,
+            | Operator::OppositeCase
+            | Operator::ToggleComments => false,
         }
     }
 }