refactor(reactivity): use more efficient reactive checks

WeakSets and WeakMaps shows degrading performance as the amount of
observed objects increases. Using hidden keys result in better
performance especially when repeatedly creating large amounts of
reactive proxies.

This also makes it possible to more efficiently declare non-reactive
objects in userland.

packages/runtime-core/src/componentProxy.ts

@@ -6,7 +6,8 @@ import {
   ReactiveEffect,
   UnwrapRef,
   toRaw,
-  shallowReadonly
+  shallowReadonly,
+  ReactiveFlags
 } from '@vue/reactivity'
 import {
   ExtractComputedReturns,
@@ -128,6 +129,11 @@ export const PublicInstanceProxyHandlers: ProxyHandler<any> = {
       appContext
     } = instance
 
+    // let @vue/reatvitiy know it should never observe Vue public instances.
+    if (key === ReactiveFlags.skip) {
+      return true
+    }
+
     // data / props / ctx
     // This getter gets called for every property access on the render context
     // during render and is a major hotspot. The most expensive part of this
@@ -197,10 +203,9 @@ export const PublicInstanceProxyHandlers: ProxyHandler<any> = {
     } else if (
       __DEV__ &&
       currentRenderingInstance &&
-      // #1091 avoid isRef/isVNode checks on component instance leading to
-      // infinite warning loop
-      key !== '_isRef' &&
-      key !== '_isVNode'
+      // #1091 avoid internal isRef/isVNode checks on component instance leading
+      // to infinite warning loop
+      key.indexOf('__v') !== 0
     ) {
       if (data !== EMPTY_OBJ && key[0] === '$' && hasOwn(data, key)) {
         warn(