Allow break keyword to break out of deeply nested loops

[blackears]

When you use the break keyword, it currently only breaks out of the innermost loop it is used in. It would be useful if there was a way to be able to break out of more deeply nested loops. Some languages use a label syntax to do this. Maybe something like:

@label outer_loop
for i in my_list.size():
    while foo < 10:
        if my_condition(foo, bar):
            break outer_loop
        foo += 1

[AThousandShips]

Already tracked by #3780

[Calinou]

This is already being tracked in #3780.