libbinder: mix and match binderRpcTest client and services

For every combination of single/multi-threaded and
kernel/no-kernel binderRpcTest, run every possible client
combination against every combination of service.

To make this possible, we split the service code into 4
separate executables (one per combination) and have
the client code run each specific service using execl().

Bug: 224644083
Test: atest binderRpcTest
Change-Id: Ie95a70c241be7dcfefc51f56b8d9ed95a864b860