[TS] generated typescript should be conformant to isolatedDeclarations and isolatedModules requirements

[bjornharrtell]

See https://www.typescriptlang.org/tsconfig/#isolatedDeclarations and https://www.typescriptlang.org/tsconfig/#isolatedModules.

This improves TypeScript typing to be explicit which allows more a simple type analysis model improving performance and future compatibility in the TypeScript ecosystem.