"yield all" construction as syntactic sugar over foreach yielding of enumerables

[DinoProga]

Adding "yield all" as syntactic sugar over foreach for enumerables will make working with them more intuitive and convenient. It also resonates with patern machining, in a way close to natural language (i.e. if (value is not null)...).

        int[] values = [1, 2, 3];
        yield all values;

This code is simpler and easier to understand than the traditional foreach loop with yield return item;. It also aligns with the existing construction yield break;.

Such functionality does not require a significant change in the operating principles; it can be achieved by simply using a cyclic yield return under the hood.

[ufcpp]

Dup of #378

[CyrusNajmabadi]

Closing as dupe.