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

include/xrpl/protocol/TxMeta.h

@@ -116,7 +116,9 @@ public:
     STAmount
     getDeliveredAmount() const
     {
-        assert(hasDeliveredAmount());
+        ASSERT(
+            hasDeliveredAmount(),
+            "ripple::TxMeta::getDeliveredAmount : non-null delivered amount");
         return *mDelivered;
     }