Rename rope::ChunksIter to rope::Chunks

This is consistent with how we name the other chunk iterators.

zed/src/editor/display_map/fold_map.rs

@@ -669,7 +669,7 @@ impl<'a> Iterator for BufferRows<'a> {
 
 pub struct Chunks<'a> {
     transform_cursor: Cursor<'a, Transform, DisplayOffset, TransformSummary>,
-    buffer_chunks: buffer::ChunksIter<'a>,
+    buffer_chunks: buffer::Chunks<'a>,
     buffer_offset: usize,
 }