[turbofan] Introduce JSCallForwardVarargs operator.

src/arm64/interface-descriptors-arm64.cc

Index: src/arm64/interface-descriptors-arm64.cc
diff --git a/src/arm64/interface-descriptors-arm64.cc b/src/arm64/interface-descriptors-arm64.cc
index b0a80c636f5905b67200d092254e326a180febde..78ede962e08098d47baa40836bbd527c4925202e 100644
--- a/src/arm64/interface-descriptors-arm64.cc
+++ b/src/arm64/interface-descriptors-arm64.cc
@@ -200,6 +200,13 @@ void CallTrampolineDescriptor::InitializePlatformSpecific(
   data->InitializePlatformSpecific(arraysize(registers), registers);
 }
 
+void CallForwardVarargsDescriptor::InitializePlatformSpecific(
+    CallInterfaceDescriptorData* data) {
+  // x1: target
+  // x2: start index (to supported rest parameters)
+  Register registers[] = {x1, x2};
+  data->InitializePlatformSpecific(arraysize(registers), registers);
+}
 
 void ConstructStubDescriptor::InitializePlatformSpecific(
     CallInterfaceDescriptorData* data) {