Add BuiltinIteratorReturn to IterableIterator and AsyncIterableIterator return types

[rbuckton]

This is a follow-on PR to https://github.com/microsoft/TypeScript/pull/58243 to add BuiltinIteratorReturn to all IterableIterator and AsyncIterableIterator return types.

TODO:

• [ ] Update the "typescript" dependency in package.json to a shipping version that supports BuiltinIteratorReturn and the TReturn type parameter for IterableIterator/AsyncIterableIterator
• [ ] Update README.md to indicate the minimum TypeScript version