refactor(reactivity): move array ref handling into getter

packages/reactivity/src/reactive.ts

@@ -9,7 +9,7 @@ import {
   mutableCollectionHandlers,
   readonlyCollectionHandlers
 } from './collectionHandlers'
-import { UnwrapRef, Ref, isRef } from './ref'
+import { UnwrapRef, Ref } from './ref'
 import { makeMap } from '@vue/shared'
 
 // WeakMaps that store {raw <-> observed} pairs.
@@ -46,9 +46,6 @@ export function reactive(target: object) {
   if (readonlyToRaw.has(target)) {
     return target
   }
-  if (isRef(target)) {
-    return target
-  }
   return createReactiveObject(
     target,
     rawToReactive,