Pass Summary::Context to Item::summarize (#18510)

We are going to use this in the multi-buffer to produce a summary for an
`Excerpt` that contains a `Range<Anchor>`.

Release Notes:

- N/A

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

crates/editor/src/display_map/inlay_map.rs

@@ -74,7 +74,7 @@ impl Inlay {
 impl sum_tree::Item for Transform {
     type Summary = TransformSummary;
 
-    fn summary(&self) -> Self::Summary {
+    fn summary(&self, _cx: &()) -> Self::Summary {
         match self {
             Transform::Isomorphic(summary) => TransformSummary {
                 input: summary.clone(),