Interop Gen: Support Interfaces

This issue is to add support to the Dart TS Declaration Interop Gen tool to support TS interfaces.

Interfaces are represented as anonymous objects (unimplemented) or are implemented by classes:
```ts
export interface A {
  p: number;
  c: string;
  control(a: number): void;
}
```

This issue will also require the refactoring of variables and functions to consider properties and methods.
