Start on adding support for editing via the assistant panel (#14795)

Note that this shouldn't have any visible user-facing behavior yet. The
feature is incomplete but we wanna merge early to avoid a long-running
branch.

Release Notes:

- N/A

---------

Co-authored-by: Nathan <nathan@zed.dev>

crates/languages/src/rust/outline.scm

@@ -16,7 +16,8 @@
     "impl" @context
     trait: (_)? @name
     "for"? @context
-    type: (_) @name) @item
+    type: (_) @name
+    body: (_ "{" @open (_)* "}" @close)) @item
 
 (trait_item
     (visibility_modifier)? @context