Add integration test for typescript type definitions (d.ts)

Issue #1998 was found when trying to use the type definitions with the TypeScript compiler. Maybe it would be a good idea to add add a small integration test that can be run in CI for testing the type definitions. A minimal JavaScript project that uses some type definitions generated from Gleam code and tries to compile with the TypeScript compiler. Probably this doesn't need to be done on all the cross-compilation targets, but unsure what is the easiest way to integrate this in the current CI pipeline.