Convert `int` or `TensorImageSize` to (height,width) of an image.

def tis2hw(size:Union[int,TensorImageSize]) -> Tuple[int,int]:
    "Convert `int` or `TensorImageSize` to (height,width) of an image."
    if type(size) is str: raise RuntimeError("Expected size to be an int or a tuple, got a string.")
    return listify(size, 2) if isinstance(size, int) else listify(size[-2:],2)