[epic] Builder pattern for TypeScript objects and types

[rbalicki2]

Initial thoughts... I would imagine we have:

• the underlying source of truth, a btreemap of fields or whatever
• some way to iterate/fold the btreemap, ideally in a typesafe manner
  from this, we would do one of two things:
• either generate a string using a nice API, e.g. enter_object("field_name"), write_field("__typename", "ConcreteNameOfType"), etc), or
• (probably better) generate a TSObject type and do stuff like .enter_object("field_name") etc, and then have that TSObject know how to stringify itself in a way that works for all of our generated files

I guess ideally, the TSObject is the entire pre-stringified artifact

Maybe one of these will work for us

• https://docs.rs/oxc/latest/oxc/ast/index.html
• https://github.com/dat2/ecmascript/blob/master/src/ast.rs#L149