vim: { } to navigate by paragraph (#2668)

As part of this I added `assert_shared_state()` to the
NeovimBackedTestContext so that it is more like a drop-in replacement
for the VimTestContext.

The remaining part of zed-industries/community#682 is adding bracket
matching to plain text. It looks like the current logic requires there
to be a tree sitter language for the language in order to support
bracket matching. I didn't fix this in this PR because I was unsure
whether to try and work around that, or to try and add a plain text tree
sitter language.

Release Notes:

- vim: support `{` and `}` for paragraph motion
([#470](https://github.com/zed-industries/community/issues/470)).
- vim: fix `%` at the end of the line
([#682](https://github.com/zed-industries/community/issues/682)).

crates/editor/src/editor.rs

@@ -5123,7 +5123,7 @@ impl Editor {
         self.change_selections(Some(Autoscroll::fit()), cx, |s| {
             s.move_with(|map, selection| {
                 selection.collapse_to(
-                    movement::start_of_paragraph(map, selection.head()),
+                    movement::start_of_paragraph(map, selection.head(), 1),
                     SelectionGoal::None,
                 )
             });
@@ -5143,7 +5143,7 @@ impl Editor {
         self.change_selections(Some(Autoscroll::fit()), cx, |s| {
             s.move_with(|map, selection| {
                 selection.collapse_to(
-                    movement::end_of_paragraph(map, selection.head()),
+                    movement::end_of_paragraph(map, selection.head(), 1),
                     SelectionGoal::None,
                 )
             });
@@ -5162,7 +5162,10 @@ impl Editor {
 
         self.change_selections(Some(Autoscroll::fit()), cx, |s| {
             s.move_heads_with(|map, head, _| {
-                (movement::start_of_paragraph(map, head), SelectionGoal::None)
+                (
+                    movement::start_of_paragraph(map, head, 1),
+                    SelectionGoal::None,
+                )
             });
         })
     }
@@ -5179,7 +5182,10 @@ impl Editor {
 
         self.change_selections(Some(Autoscroll::fit()), cx, |s| {
             s.move_heads_with(|map, head, _| {
-                (movement::end_of_paragraph(map, head), SelectionGoal::None)
+                (
+                    movement::end_of_paragraph(map, head, 1),
+                    SelectionGoal::None,
+                )
             });
         })
     }