Use virtual scroller for diffs file tree

What does this MR do and why?

Implements Use Virtual Scrolling on the Diffs File Tree (#386703 - closed).

Fixes Improve browser Total Blocking Time (TBT) perfo... (#338359 - closed).

This MR adds virtual scrolling rendering to diffs file tree to improve page performance.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Open any large MR Changes page (GDK example)
2. Open file tree ()
3. You should see a file tree properly render:

Example file tree screenshot

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.