[Feature Request] Vue instance method support

[weihongyu12]

Problem to solve

In many cases, we need to make some information in the js file, but we can't use the vue component at this time, because the component is not yet mounted.

We need some support for instance methods so that we can call them in Vue components and JS files.

In Vuetify, the components that need to be supported are:

VDialog

VSnackbar

Proposed solution

In the JS file, we can use it like this:

import { VDialog, VSnackbar } form 'vuetify';

VDialog(options);
VSnackbar(options);

In the Vue component, we can use it like this:

this.$dialog(options);
this.$snackbar(options);

[KaelWD]

Duplicate of #2384, #3037