fix(startWith): fix incorrect types (#5157)
fix(startWith): fix incorrect types (#5157)

This change does not effect the user-facing function overloads, so the function's public signature remains unchanged. This incorrect typing was visible in the docs however, so this change can be thought of as a documentation change.
martinsik/rxjs,martinsik/rxjs,trxcllnt/RxJS,ReactiveX/rxjs,benlesh/RxJS,ReactiveX/RxJS,ReactiveX/RxJS,ReactiveX/rxjs,kwonoj/RxJS,ReactiveX/RxJS,kwonoj/RxJS,ReactiveX/rxjs,trxcllnt/RxJS,martinsik/rxjs,benlesh/RxJS,martinsik/rxjs,kwonoj/RxJS,ReactiveX/RxJS,kwonoj/RxJS,ReactiveX/rxjs,trxcllnt/RxJS,benlesh/RxJS,benlesh/RxJS,trxcllnt/RxJS