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/git/src/diff.rs

@@ -34,7 +34,7 @@ struct InternalDiffHunk {
 impl sum_tree::Item for InternalDiffHunk {
     type Summary = DiffHunkSummary;
 
-    fn summary(&self) -> Self::Summary {
+    fn summary(&self, _cx: &text::BufferSnapshot) -> Self::Summary {
         DiffHunkSummary {
             buffer_range: self.buffer_range.clone(),
         }