feat(expose): always expose $ instance properties on child refs

packages/runtime-core/__tests__/apiExpose.spec.ts

@@ -7,7 +7,7 @@ describe('api: expose', () => {
       render() {},
       setup(_, { expose }) {
         expose({
-          foo: ref(1),
+          foo: 1,
           bar: ref(2)
         })
         return {
@@ -169,4 +169,26 @@ describe('api: expose', () => {
     const root = nodeOps.createElement('div')
     render(h(Parent), root)
   })
+
+  test('expose should allow access to built-in instance properties', () => {
+    const Child = defineComponent({
+      render() {
+        return h('div')
+      },
+      setup(_, { expose }) {
+        expose()
+        return {}
+      }
+    })
+
+    const childRef = ref()
+    const Parent = {
+      setup() {
+        return () => h(Child, { ref: childRef })
+      }
+    }
+    const root = nodeOps.createElement('div')
+    render(h(Parent), root)
+    expect(childRef.value.$el.tag).toBe('div')
+  })
 })