[clr-interp] Handle some forms of unboxing stub (#118501)

When encountering an UnboxingStub to execute, invoke it as a compiled method instead of as a interpreted one

Author: davidwrighton

src/coreclr/vm/interpexec.cpp

@@ -1973,7 +1973,7 @@ void InterpExecMethod(InterpreterFrame *pInterpreterFrame, InterpMethodContextFr
                             pInterpreterFrame->SetTopInterpMethodContextFrame(pFrame);
                             GCX_PREEMP();
                             // Attempt to setup the interpreter code for the target method.
-                            if (targetMethod->IsIL() || targetMethod->IsNoMetadata())
+                            if ((targetMethod->IsIL() || targetMethod->IsNoMetadata()) && !targetMethod->IsUnboxingStub())
                             {
                                 targetMethod->PrepareInitialCode(CallerGCMode::Coop);
                             }