editor: Speed up colorize_brackets slightly in large multibuffers (#43713)

There is still room for improvement here as `anchor(s)_in_excerpt` is
generally a bad API here due to it reseeking the entire excerpt tree
from the start on every call which we don't really need. But this at
least cuts the seeks down by a factor of 4 for now.

Release Notes:

- Improved performance of bracket colorization in large multibuffers

crates/multi_buffer/src/multi_buffer.rs

@@ -5084,8 +5084,8 @@ impl MultiBufferSnapshot {
         let excerpt = self.excerpt(self.latest_excerpt_id(excerpt_id))?;
 
         Some(
-            self.anchor_in_excerpt_(excerpt, text_anchor.start)?
-                ..self.anchor_in_excerpt_(excerpt, text_anchor.end)?,
+            Self::anchor_in_excerpt_(excerpt, text_anchor.start)?
+                ..Self::anchor_in_excerpt_(excerpt, text_anchor.end)?,
         )
     }
 
@@ -5097,10 +5097,24 @@ impl MultiBufferSnapshot {
         text_anchor: text::Anchor,
     ) -> Option<Anchor> {
         let excerpt = self.excerpt(self.latest_excerpt_id(excerpt_id))?;
-        self.anchor_in_excerpt_(excerpt, text_anchor)
+        Self::anchor_in_excerpt_(excerpt, text_anchor)
     }
 
-    fn anchor_in_excerpt_(&self, excerpt: &Excerpt, text_anchor: text::Anchor) -> Option<Anchor> {
+    /// Same as [`MultiBuffer::anchor_in_excerpt`], but more efficient than calling it multiple times.
+    pub fn anchors_in_excerpt(
+        &self,
+        excerpt_id: ExcerptId,
+        text_anchors: impl IntoIterator<Item = text::Anchor>,
+    ) -> Option<impl Iterator<Item = Option<Anchor>>> {
+        let excerpt = self.excerpt(self.latest_excerpt_id(excerpt_id))?;
+        Some(
+            text_anchors
+                .into_iter()
+                .map(|text_anchor| Self::anchor_in_excerpt_(excerpt, text_anchor)),
+        )
+    }
+
+    fn anchor_in_excerpt_(excerpt: &Excerpt, text_anchor: text::Anchor) -> Option<Anchor> {
         match text_anchor.buffer_id {
             Some(buffer_id) if buffer_id == excerpt.buffer_id => (),
             Some(_) => return None,