feat(reactivity): proxyRefs method and ShallowUnwrapRefs type (#1682)

* feat(reactivity): `proxyRefs` method and `ShallowUnwrapRefs` type

BREAKING CHANGE: template auto ref unwrapping are now applied shallowly,
i.e. only at the root level. See https://github.com/vuejs/vue-next/pull/1682 for
more details.

packages/runtime-core/src/component.ts

@@ -1,10 +1,10 @@
 import { VNode, VNodeChild, isVNode } from './vnode'
 import {
-  reactive,
   ReactiveEffect,
   pauseTracking,
   resetTracking,
-  shallowReadonly
+  shallowReadonly,
+  proxyRefs
 } from '@vue/reactivity'
 import {
   CreateComponentPublicInstance,
@@ -548,7 +548,7 @@ export function handleSetupResult(
     }
     // setup returned bindings.
     // assuming a render function compiled from template is present.
-    instance.setupState = reactive(setupResult)
+    instance.setupState = proxyRefs(setupResult)
     if (__DEV__) {
       exposeSetupStateOnRenderContext(instance)
     }