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/outline_panel/src/outline_panel.rs

@@ -2410,11 +2410,9 @@ impl OutlinePanel {
         editor: &View<Editor>,
         cx: &mut ViewContext<Self>,
     ) -> Option<PanelEntry> {
-        let selection = editor
-            .read(cx)
-            .selections
-            .newest::<language::Point>(cx)
-            .head();
+        let selection = editor.update(cx, |editor, cx| {
+            editor.selections.newest::<language::Point>(cx).head()
+        });
         let editor_snapshot = editor.update(cx, |editor, cx| editor.snapshot(cx));
         let multi_buffer = editor.read(cx).buffer();
         let multi_buffer_snapshot = multi_buffer.read(cx).snapshot(cx);