Add readStrongBinder that takes an interface

We use a template function to let us pass arbitrary interfaces, all of which
can be cast to IBinder.

Test: unit tests
Bug: 23600713
Signed-off-by: Casey Dahlin <sadmac@google.com>

(cherry picked from commit f0c13772)

Change-Id: I69e8b534343c299c25cfb591dbdf122860c9ccc5