parcel: Add efficient methods for writing and reading a parcelable.

The documentation used to recommend calling Parcelable.writeToParcel
instead of using the Parcel API for sending Parcelable types.
This leaves the developer to have to deal with null values and makes
it harder to create tools that generate correct efficient code.
I suggest that we add a these 2 methods:
   writeTypedObject and createTypedObject
as an alternative.

Change-Id: I85443417909dcb9590d3f0a72f0130a4da4ead38