Extract run_rpc_server to libbinder_common

We have two very similar uses of RunRpcServerCallback; extract them to
a common place, using a closure to encapsulate the specific behavior
for notifiying readiness.

This also neatly encapsulates all the unsafe code, and justification
of it, in one place.

Bug: 187444679
Test: atest ComposTestCase
Change-Id: If23f862748b2f921690820eaa6ee80e4b2829274
diff --git a/binder_common/lib.rs b/binder_common/lib.rs
index 055688a..f2391e3 100644
--- a/binder_common/lib.rs
+++ b/binder_common/lib.rs
@@ -17,6 +17,7 @@
 //! Common items useful for binder clients and/or servers.
 
 pub mod lazy_service;
+pub mod rpc_server;
 
 use binder::public_api::{ExceptionCode, Status};
 use std::ffi::CString;