Generate RBI/RBS files for `Interface` and `Constant` types

[paracycle]

Now that the generator of the Interface and Constant types is Ruby code, we can start generating signatures for the arguments and getters for Interface types and similarly type the values of the Constant entries.

We can do this by generating RBS and/or RBI files for the classes/modules we are generating that the library can export, so that consumers can get a better experience in their editors.