refactor(runtime-core): revert setup() result reactive conversion

BREAKING CHANGE: revert setup() result reactive conversion

    Revert 6b10f0c & a840e7d. The motivation of the original change was
    avoiding unnecessary deep conversions, but that can be achieved by
    explicitly marking values non-reactive via `markNonReactive`.

    Removing the reactive conversion behavior leads to an usability
    issue in that plain objects containing refs (which is what most
    composition functions will return), when exposed as a nested
    property from `setup()`, will not unwrap the refs in templates. This
    goes against the "no .value in template" intuition and the only
    workaround requires users to manually wrap it again with `reactive()`.

    So in this commit we are reverting to the previous behavior where
    objects returned from `setup()` are implicitly wrapped with
    `reactive()` for deep ref unwrapping.

packages/runtime-core/src/component.ts

@@ -1,5 +1,6 @@
 import { VNode, VNodeChild, isVNode } from './vnode'
 import {
+  reactive,
   ReactiveEffect,
   shallowReadonly,
   pauseTracking,
@@ -398,7 +399,7 @@ export function handleSetupResult(
     }
     // setup returned bindings.
     // assuming a render function compiled from template is present.
-    instance.renderContext = setupResult
+    instance.renderContext = reactive(setupResult)
   } else if (__DEV__ && setupResult !== undefined) {
     warn(
       `setup() should return an object. Received: ${
@@ -474,10 +475,6 @@ function finishComponentSetup(
     currentInstance = null
     currentSuspense = null
   }
-
-  if (instance.renderContext === EMPTY_OBJ) {
-    instance.renderContext = {}
-  }
 }
 
 // used to identify a setup context proxy