Add Antithesis intrumentation (#5042)

* Copy Antithesis SDK version 0.4.0 to directory external/
* Add build option `voidstar` to enable instrumentation with Antithesis SDK
* Define instrumentation macros ASSERT and UNREACHABLE in terms of regular C assert
* Replace asserts with named ASSERT or UNREACHABLE
* Add UNREACHABLE to LogicError
* Document instrumentation macros in CONTRIBUTING.md

src/xrpld/app/main/GRPCServer.cpp

@@ -606,7 +606,7 @@ GRPCServer::stop()
 
 GRPCServer::~GRPCServer()
 {
-    assert(!running_);
+    ASSERT(!running_, "ripple::GRPCServer::~GRPCServer : is not running");
 }
 
 }  // namespace ripple