[clr-interp] Async Resume stubs are exclusive to the JIT as they use a set of intrinsics that are JIT specific (#123046)

Implement the second half of the intrinsic for SetNextCallAsyncContinuation. This allows the interpreter to correctly generate code for async resumption stubs (although it won't use them itself, as the interpreter has a different path for calling async resume stubs that we don't currently plan to remove. This is used in some of our interpreter test modes where the runtime may choose to JIT a runtime async method and interpret its associated async resumption stub.

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Co-authored-by: Jan Kotas <jkotas@microsoft.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: 3 people

src/coreclr/interpreter/compiler.cpp

@@ -4949,8 +4949,18 @@ void InterpCompiler::EmitCall(CORINFO_RESOLVED_TOKEN* pConstrainedToken, bool re
         m_pStackPointer--;
         int32_t continuationArg = m_pStackPointer[0].var;
 
-        AddIns(INTOP_LDNULL);
-        m_pLastNewIns->SetDVar(continuationArg);
+        if (m_nextCallAsyncContinuationVar == -1)
+        {
+            AddIns(INTOP_LDNULL);
+            m_pLastNewIns->SetDVar(continuationArg);
+        }
+        else
+        {
+            AddIns(INTOP_MOV_P);
+            m_pLastNewIns->SetSVar(m_nextCallAsyncContinuationVar);
+            m_pLastNewIns->SetDVar(continuationArg);
+            m_nextCallAsyncContinuationVar = -1;
+        }
         callArgs[continuationArgLocation] = continuationArg;
     }