Slightly simplify editor highlights code (#9123)

Prepare for git diff hunk highlights by grouping all inlay highlight
properties into one struct, and removing the dead background highlight
code.


Release Notes:

- N/A
597465b0f5Kirill Bulatov committed on 3/9/2024, 10:38:45 PM· committed by GitHubparentccc9391
4 files changedLine totals unavailable