libbinderwrapper: Add BinderWrapper::GetOrCreateInstance()

In libraries relying on binder it is useful to be able to obtain an
existing copy of BinderWrapper or create one if it doesn't exist.

This allows to abstract the actual RPC (binder) from clients who have
no other dependencies on this RPC.

BUG: 23782171
Change-Id: Ie775d3d8ab83d75e38abc7e1385eb39a363555ef