Exempt partitioned function calls from the Placer's constraint on resource

inputs.

PartitionedCallOp never dereferences resource inputs; it instead forwards them
to appropriately placed primitive ops. The exemption is encoded directly in
placer.cc (instead of, e.g., in the OpDef proto) because PartitionedCall, along
with its stateful counterpart, are as of now the only TensorFlow ops that
benefit from this exemption.

PiperOrigin-RevId: 203537953