Produce .ts output

[Jand42]

TypeScript output overall shape would follow current JavaScript output exactly (https://github.com/dotnet-websharper/core/blob/master/docs/WebSharper8Translation.md), except with extra annotations for typing, casts and coercions.

So they can be perceived as a combination of 3 elements:

• The JavaScript output with type annotations
• The function signatures that are making up the .d.ts output
• Casts and coercions which are only necessary for TS correctness, but are erased for JavaScript