editor: Restore selections to positions after last edit (#28527)

Closes #22692

Makes it so when undoing a format operation, the selections are set to
where they were at the last edit.

Release Notes:

- Made it so the cursor position is reset to where it was after the last
edit when undoing a format operation. This will only result in different
behavior when you make an edit, scroll away, initiate formatting (either
by saving or manually) and then undo the format.

---------

Co-authored-by: Zed AI <ai@zed.dev>

crates/multi_buffer/src/multi_buffer.rs

@@ -1118,9 +1118,16 @@ impl MultiBuffer {
         self.history.start_transaction(now)
     }
 
-    pub fn last_transaction_id(&self) -> Option<TransactionId> {
-        let last_transaction = self.history.undo_stack.last()?;
-        return Some(last_transaction.id);
+    pub fn last_transaction_id(&self, cx: &App) -> Option<TransactionId> {
+        if let Some(buffer) = self.as_singleton() {
+            return buffer.read_with(cx, |b, _| {
+                b.peek_undo_stack()
+                    .map(|history_entry| history_entry.transaction_id())
+            });
+        } else {
+            let last_transaction = self.history.undo_stack.last()?;
+            return Some(last_transaction.id);
+        }
     }
 
     pub fn end_transaction(&mut self, cx: &mut Context<Self>) -> Option<TransactionId> {