Typing of the race operator

[timdeschryver]

Bug Report

Current Behavior
Currently, the typing is the following:

const o = of('a', 'b', 'c').pipe(race(of('x', 'y', 'z'), [of('t', 'i', 'm')])); // $ExpectType Observable<string>

Expected behavior

While it should be:

const o = of('a', 'b', 'c').pipe(race(of('x', 'y', 'z'), [of('t', 'i', 'm')])); // $ExpectType Observable<string|Observable<string>>

Environment

• RxJS version: 6.3.3

Additional context/Screenshots

See #4344 (comment)