binder_rs: Add Parcelable trait

Adds Parcelable trait that all auto-generated Rust parcelables
implement. This trait provides the get_descriptor() and
get_stability(), as well as internal serialization and
deserialization methods specific to parcelables.

Bug: 169035750
Test: m
Change-Id: Ib97ac4d79cd9829ab3968076492ac1f28f27e8ff