libbinder: fuzzer for RPC server

Fuzz sending arbitrary commands to a single connection on a single RPC
server.

Future considerations:
- support fuzzing multiple clients w/ multiple connections
- better way to wait for a service to shutdown

Bug: 182938024
Test: fuzzer can run for a few minutes w/o crashing
Change-Id: Ifc1da577208ba1effb02fa33b0b30fd5cfd98d9e