Skip over folded regions when iterating over multibuffer chunks (#15646)

This commit weaves through new APIs for language::BufferChunks, multi_buffer::MultiBufferChunks and inlay_map::InlayChunks that allow seeking with an upper-bound. This allows us to omit doing syntax highligting and looking up diagnostics for folded ranges. This in turn directly improves performance of assistant panel with large contexts.

Release Notes:

- Fixed poor performance when editing in the assistant panel after
inserting large files using slash commands

---------

Co-authored-by: Max <max@zed.dev>
Co-authored-by: Max Brunsfeld <maxbrunsfeld@gmail.com>

crates/rope/src/rope.rs

@@ -615,6 +615,11 @@ impl<'a> Chunks<'a> {
         self.offset = offset;
     }
 
+    pub fn set_range(&mut self, range: Range<usize>) {
+        self.range = range.clone();
+        self.seek(range.start);
+    }
+
     /// Moves this cursor to the start of the next line in the rope.
     ///
     /// This method advances the cursor to the beginning of the next line.