Investigate ways to reduce 'flickering' when scrolling through large source files

Description

In !82806 (merged) we introduced a way to handle very large source files by splitting source code into chunks and only highlighting the chunks that are visible to the user.

Since we only highlight what is visible to the user there is a slight flicker when scrolling through a large source file.

This issue is a proposal to investigate ways that we can reduce the flickering. Perhaps we can display unhighlighted content initially and then switch to the highlighted content. Or perhaps display a gray background behind the line numbers as suggested here.

Preview

Here's a file with 100,000 lines of code: