Fix optional values in generated typescript classes

Currently we need to provide all properties when creating instances of types. TypeScript doesn't seem to allow class-level fields to be optional so need to see what the options are (properties instead of fields? constructors?). Example here.

This appears to not be possible without constructors etc. (and the sample links here was bad, that's an VSCode class, not one of ours!).

Removed some TODOs.