chore: add warning if multiple vue instances are loaded
chore: add warning if multiple vue instances are loaded

see #4068

Webifi/vuetify,Webifi/vuetify,vuetifyjs/vuetify,Webifi/vuetify,Phlow2001/vuetify,Phlow2001/vuetify,Phlow2001/vuetify,vuetifyjs/vuetify,Phlow2001/vuetify,vuetifyjs/vuetify,vuetifyjs/vuetify