[promises] Move CreateResolvingFunctions to c++

src/factory.h

Index: src/factory.h
diff --git a/src/factory.h b/src/factory.h
index 7711c32ae566640824c95db7f9237bf3412a18c8..5f0a54f72524d831db8ff6420e1ddd5cde22ab0e 100644
--- a/src/factory.h
+++ b/src/factory.h
@@ -310,6 +310,8 @@ class V8_EXPORT_PRIVATE Factory final {
   Handle<Context> NewBlockContext(Handle<JSFunction> function,
                                   Handle<Context> previous,
                                   Handle<ScopeInfo> scope_info);
+  // Create a promise context.
+  Handle<Context> NewPromiseResolvingFunctionContext(int length);
 
   // Allocate a new struct.  The struct is pretenured (allocated directly in
   // the old generation).