Resolves the payload format and a DataView URI for given artifacts.
) -> Tuple[int, Optional[Text]]
This routine make sure that the provided list of Examples artifacts are of
the same payload type, and if their payload type is FORMAT_PROTO, it resolves
one DataView (if applicable) to be used to access the data in all the
artifacts in a consistent way (i.e. the RecordBatches from those artifacts
will have the same schema).
A list of Examples artifact.
A pair. The first term is the payload format (a value in
example_gen_pb2.PayloadFormat enum); the second term is the URI to the
resolved DataView (could be None, if the examples are not FORMAT_PROTO,
or they are all FORMAT_PROTO, but all do not have a DataView attached).
if not all artifacts are of the same payload format, or
if they are all of FORMAT_PROTO but some (but not all) of them do not
have a DataView attached.