languages: what is responsible for auto-indenting new {} blocks?

[spaceunifyfifty]

Most languages will automatically insert a newline and tab when pressing Enter while inbetween { }.
TypeScript for example:

I'm trying to get this working for Kotlin detailed at zed-extensions/kotlin#5. I have newline insertion working, but can't figure out which config file controls the tab insertion. or if an entire language server protocol / formatter needs to be implemented for that behavior. Anyone know?