this change introduces a new class LightFlattenable<> which is
a protocol to flatten simple objects that don't require
binders or file descriptors; the benefit of this protocol is that
it doesn't require the objects to have a virtual table and give us
a consitant way of doing this.
we also introduce an implementation of this protocol for
POD structures, LightFlattenablePod<>.
Parcel has been update to handle this protocol automatically.
Sensor, Rect, Point and Region now use this new protocol.
Change-Id: Icb3ce7fa1d785249eb666f39c2129f2fc143ea4a
2497a1524d