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.

test-dts/defineComponent.test-d.tsx

@@ -4,7 +4,6 @@ import {
   defineComponent,
   PropType,
   ref,
-  Ref,
   reactive,
   createApp
 } from './index'
@@ -65,15 +64,12 @@ describe('with object props', () => {
       // setup context
       return {
         c: ref(1),
-        d: reactive({
+        d: {
           e: ref('hi')
-        }),
+        },
         f: reactive({
           g: ref('hello' as GT)
-        }),
-        h: {
-          i: ref('hi')
-        }
+        })
       }
     },
     render() {
@@ -106,9 +102,6 @@ describe('with object props', () => {
       expectType<string>(this.d.e)
       expectType<GT>(this.f.g)
 
-      // should not unwrap refs nested under non-reactive objects
-      expectType<Ref<string>>(this.h.i)
-
       // setup context properties should be mutable
       this.c = 2