Add "yield return!" like "return!" in F#

[Raneddo]

There is yield statement now and it's very useful in LINQ, but more and more often processing of IEnumerable's divides to batches.

Now it looks like

// batch from morelinq
var batches = GetFeed(from, to).Batch(1000);

foreach (var batch in batches) {
    var values = GetValuesByOther(batches); // returns IEnumerable of other type
    
    foreach (var val in values) {
        yield return val;
    }
}

I suggest to make something like this

var batches = GetFeed(from, to).Batch(1000);

foreach (var batch in batches) {
    var values = GetValuesByOther(batches); // returns IEnumerable of other type
    yield return! values;
}

There are this construction in F# and other functional languages. And will be useful in OOP C#

[HaloFour]

See: #378