Provide backward compatibility in Vue.createMwApp() for the store
option. Vuex 4 expects Vue.createMwApp(...).use(store), but code written
for Vuex 3 will do Vue.createMwApp({..., store: store }) instead.
Unfortunately, it doesn't appear to be possible to provide backward
compatibiltiy for new Vue( { ..., store: store } ) . I can't find a way
to access the underlying app instance.
Bug: T289102
Change-Id: I21641827780f4a7d8a5196c7dab14fbc3e4f4175
