Object arguments for combineLatest and forkJoin

[rraziel]

Feature Request

Is your feature request related to a problem? Please describe.
When extensively using combineLatest or forkJoin, especially with many arguments, it can be cumbersome to have the result as an array (e.g. you can't pluck) and I typically end up having a single:

map(([a,b,c]) => ({a,b,c}))

Except it can be with many arguments and their names are obviously longer.

Moreover, the result of a combineLatest(a,b,c) (with 7+ arguments) is a [typeof(a)|typeof(b)|typeof(c)], which is not very type-safe, e.g.:

combineLatest([
  of(true),
  of('hello world'),
  of(42)
]).pipe(
  map(([a, b, c]) => {
    // a is boolean|string|number
    // b is boolean|string|number
    // c is boolean|string|number
  })
);

Describe the solution you'd like
On top of taking an array, combineLatest and forkJoin could take an object where each field is an Observable. It would then return an object with what the observable emitted, e.g:

combineLatest({
  a: of(true),
  b: of('hello world'),
  c: of(42)
}).pipe(
  map(({a, b, c}) => ({
    // a is boolean
    // b is string
    // c is number
  })
);

Describe alternatives you've considered
Writing a pipable operator, however due to TypeScript limitations there is not much that can be done to turn the array into an object, especially after combineLatest and forkJoin already lost most of the type information for each array element.

[kwonoj]

I believe this is dupe of #5022 .