Provide ability for language services to obtain module typescript definition.

[Oceanswave]

Thinking this would consist of the following:

• Add method to module interface -- GetModuleDefinition -- returns a string in the .d.ts format.
• Add capability for converters/typeconverters to auto-generate definition.

Things like the built-in script-based modules would return the corresponding .d.ts from their original repos or @types.