[rpc_binder] Implement RPC binder over init-managed Unix domain socket

This implements an RPC binder over init-managed Unix domain sockets.
The cl adds binder tests and the new API is also used for
vm_payload_service inside Microdroid.
A previous cl aosp/2229557 sets up the binder over anonymous Unix sockets.

Test: atest MicrodroidTests ComposHostTestCases
Bug: 222479468
Change-Id: I0c7c38f4792c4536f5f88eb7e035091505f782f7
diff --git a/libs/binder/libbinder_rpc_unstable.map.txt b/libs/binder/libbinder_rpc_unstable.map.txt
index 347831a..f9c7bcf 100644
--- a/libs/binder/libbinder_rpc_unstable.map.txt
+++ b/libs/binder/libbinder_rpc_unstable.map.txt
@@ -3,6 +3,8 @@
     RunVsockRpcServer;
     RunVsockRpcServerCallback;
     VsockRpcClient;
+    RunInitUnixDomainRpcServer;
+    UnixDomainRpcClient;
     RpcPreconnectedClient;
   local:
     *;