Add type transformation

[brxck]

This should allow referencing type declarations and annotations in Typescript, as I brought up in #24

The transformation can be used on variable declarations, parameters, functions, and properties within type declarations.

This doesn't cover generics, i.e. type parameters or arguments. I started on them, but they complicate things a bit more. Personally I don't think I'm going to miss supporting them at least for now.

Any tweaks or feedback welcome 👍🏼

Closes #24

[pokey]

Awesome!! Tested locally and it works well. I had an idea for some fancy unification; lmk if you can get that approach working / if it seems like a good direction

[brxck]

Got this working with your changes. Pulling out the type node isn't quite as clean as you might hope, but all the pieces seem to fit together nicely.

[pokey]

This looks awesome @brxck. I left one more nit to make things slightly clearer but then it's good to go. I can pull it down to mess around with tomorrow my time then I'll ship it

[pokey]

Ok I pulled this one locally and it works pretty well. One that I noticed tho:

export type DecorationMap = {
  [k in SymbolColor]?: vscode.TextEditorDecorationType;
};

If cursor is inside vscode, I think I'd expect it to select vscode.TextEditorDecorationType, but it selects the whole type instead. Is that expected?

[brxck]

Apparently the type of this node is different: opting_type_annotation I hadn't seen that one before. Adding it to getTypeNode seems to handle that as expected.