fix(runtime-core): use normal object as internal prototype for attrs and slots

to allow use of hasOwnProperty()
ref vuejs/core@6df53d8#r141304923

Author: yyx990803

packages/runtime-core/src/internalObject.ts

@@ -4,7 +4,7 @@
  * `Object.getPrototypeOf`. This is more performant than defining a
  * non-enumerable property. (one of the optimizations done for ssr-benchmark)
  */
-const internalObjectProto = Object.create(null)
+const internalObjectProto = {}
 
 export const createInternalObject = () => Object.create(internalObjectProto)