REF: use check_setitem_lengths in DTA.__setitem__
Turning this into a two-line check will make it easy to add to `PandasArray.__setitem__` and `Categorical.__setitem__`, at which point we'll be able to move these methods up to `NDArrayBackedExtensionArray.__setitem__`
@jbrockmendel can you add a test for the setitem case with zero-length indexer and non-zero length value (as it is clearly untested ..) updated per suggestions Thanks!