Use type mappings for inheritance

[merlinfuchs]

This allows for extending a type from package A in package B using a config like this:

// b.go

import "github.com/gzuidhof/tygo/a"

type TypeTwo {
   a.TypeOne `tstype:",required"`
}

  - path: "github.com/gzuidhof/tygo/a"
    output_path: "../web/a.gen.ts"
  - path: "github.com/gzuidhof/tygo/b"
    output_path: "../web/b.gen.ts"
    type_mappings:
      a.TypeOne: "TypeOne"
    frontmatter: |
      import { TypeOne } from "./a.gen"

[gzuidhof]

Thank you!