Take a mutable context when resolving selections (#19948)

This is a behavior-preserving change, but lays the groundwork for
expanding selections when the cursor lands inside of a "replace" block.

Release Notes:

- N/A

crates/language_tools/src/syntax_tree_view.rs

@@ -128,12 +128,14 @@ impl SyntaxTreeView {
     fn editor_updated(&mut self, did_reparse: bool, cx: &mut ViewContext<Self>) -> Option<()> {
         // Find which excerpt the cursor is in, and the position within that excerpted buffer.
         let editor_state = self.editor.as_mut()?;
-        let editor = &editor_state.editor.read(cx);
-        let selection_range = editor.selections.last::<usize>(cx).range();
-        let multibuffer = editor.buffer().read(cx);
-        let (buffer, range, excerpt_id) = multibuffer
-            .range_to_buffer_ranges(selection_range, cx)
-            .pop()?;
+        let (buffer, range, excerpt_id) = editor_state.editor.update(cx, |editor, cx| {
+            let selection_range = editor.selections.last::<usize>(cx).range();
+            editor
+                .buffer()
+                .read(cx)
+                .range_to_buffer_ranges(selection_range, cx)
+                .pop()
+        })?;
 
         // If the cursor has moved into a different excerpt, retrieve a new syntax layer
         // from that buffer.