Add support for AbortSignal to ChunkWriter

What does this MR do and why?

This MR adds AbortSignal support for ChunkWriter. This change allows us to stop HTML streaming.

How to set up and validate locally

1. Enable rapid_diffs feature flag
2. Open any merge request page with at least 10 files changed
3. Open Changes tab and add ?rapid_diffs=true to the URL, follow the new URL
4. Rapidly change your view settings: enable whitespace, switch to parallel view
5. Observe that HTML stream is cancelled using DevTools performance benchmark