Handle TSIndexedAccessType

[thchia]

There currently isn't a handler for TSIndexedAccessType:

type ABC = {
  foo: string
}

type DEF = {
  bar: ABC["foo"] // <-- indexed type
}

The output for bar is { name: "unknown" }. Expected output would be either:

{ name: "string" } or;
{ name: "ABC[\"foo\"]" }

I believe there is an ongoing discussion in #366 over which of these 2 it should be (based on whether ABC is declared as a type or an interface), but either way currently it is neither.

I'm happy to attempt a PR but I have zero experience with AST so perhaps only if this doesn't get picked up by someone more capable 😃