binder_rs: add OwnedParcel

This adds a new binder::OwnedParcel type that exclusively
contains an owned parcel, and implements Send so it
can be sent between threads. Parcel cannot implement Send
because Parcel::Borrowed could point to thread-local
C++ values, e.g., a Parcel stored on the stack.
This change is a prerequisite for both async and
thread-safe ParcelableHolder.

Bug: 200676345
Test: atest aidl_integration_test
Change-Id: I1a7b965d26cb5350576450debd7d058a6451b1f0