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/worktree/src/worktree.rs

@@ -3339,7 +3339,7 @@ impl EntryKind {
 impl sum_tree::Item for Entry {
     type Summary = EntrySummary;
 
-    fn summary(&self) -> Self::Summary {
+    fn summary(&self, _cx: &()) -> Self::Summary {
         let non_ignored_count = if self.is_ignored || self.is_external {
             0
         } else {
@@ -3434,7 +3434,7 @@ struct PathEntry {
 impl sum_tree::Item for PathEntry {
     type Summary = PathEntrySummary;
 
-    fn summary(&self) -> Self::Summary {
+    fn summary(&self, _cx: &()) -> Self::Summary {
         PathEntrySummary { max_id: self.id }
     }
 }