fix(reactivity-transform): apply transform for labelled variable declarations

ref https://github.com/vuejs/core/issues/5298#issuecomment-1017970061

packages/reactivity-transform/__tests__/__snapshots__/reactivityTransform.spec.ts.snap

@@ -10,6 +10,7 @@ exports[`$ unwrapping 1`] = `
     }))
     let c = () => {}
     let d
+    label: var e = (ref())
     "
 `;
 
@@ -34,12 +35,13 @@ exports[`$ref & $shallowRef declarations 1`] = `
 "import { ref as _ref, shallowRef as _shallowRef } from 'vue'
 
     let foo = _ref()
-    let a = _ref(1)
+    export let a = _ref(1)
     let b = _shallowRef({
       count: 0
     })
     let c = () => {}
     let d
+    label: var e = _ref()
     "
 `;