Increase rendered elements while loading files

What does this MR do and why?

In !92987 (merged) we improved the rendering time by loading the first 5 elements first, and then rendering the rest once the browser goes into an idle state.

This MR increases the number of elements being rendered first to cater for larger screen sizes.

Screenshots or screen recordings

For instance, our Sitespeed tool uses quite a large screen size, so LCP is triggered further down on the page.

LCP is still triggered early, so the original fix still works as expected.

How to set up and validate locally

1. Open a large Markdown file
2. Inspect the performance
3. LCP should still be triggered before a big render task

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.

Related to #331447