"Bracket" colorization for indent

<!-- ⚠️⚠️ Do Not Delete This! feature_request_template ⚠️⚠️ --> <!-- Please read our Rules of Conduct: https://opensource.microsoft.com/codeofconduct/ --> <!-- Please search existing issues to avoid creating duplicates. --> <!-- Describe the feature you'd like. --> Related to #136506. I am working on a custom language that doesn't use brackets, but indentation like Python. Now it would be cool if I could add support for custom highlighting, somehow like this: <img width="294" alt="Bildschirmfoto 2022-04-28 um 09 18 18" src="https://user-images.githubusercontent.com/62756994/165698348-f065984e-c32d-40b5-abcc-5328dd9ae185.png"> <img width="292" alt="Bildschirmfoto 2022-04-28 um 09 18 52" src="https://user-images.githubusercontent.com/62756994/165698440-28f7df96-614b-4433-b316-229d9405924c.png"> (I made braces transparent for this screenshot) It would be optimal if we could make it indent based, but using a language server would also work.