[turbofan] Introduce JSCallForwardVarargs operator.

src/interface-descriptors.cc

Index: src/interface-descriptors.cc
diff --git a/src/interface-descriptors.cc b/src/interface-descriptors.cc
index 26b6422f6bfc1e4d75991477b86c2ffcc39e8764..07edfcbe95509277ad46569499afaa6e5f5c4ae3 100644
--- a/src/interface-descriptors.cc
+++ b/src/interface-descriptors.cc
@@ -433,6 +433,15 @@ void CallTrampolineDescriptor::InitializePlatformIndependent(
                                       machine_types);
 }
 
+void CallForwardVarargsDescriptor::InitializePlatformIndependent(
+    CallInterfaceDescriptorData* data) {
+  // kTarget, kStartIndex
+  MachineType machine_types[] = {MachineType::AnyTagged(),
+                                 MachineType::Int32()};
+  data->InitializePlatformIndependent(arraysize(machine_types), 0,
+                                      machine_types);
+}
+
 void ConstructStubDescriptor::InitializePlatformIndependent(
     CallInterfaceDescriptorData* data) {
   // kFunction, kNewTarget, kActualArgumentsCount, kAllocationSite