libbinder: ensure entire Parcel is the same format

Extra check in preparation for versioning work/as a guard against misuse
of this API. Note - these functions are very much like constructors, but
they can't be because Parcel is that errorprone type of object which
resets its internal state (for better or worse).

Bug: 182938972
Test: binderRpcTest
Change-Id: Ibdbe8161db9d0c8fba86f1c691c73aab49b21bc0