Add Concrete.Vue.activateContextAsync()

[mlocati]

When we need to use the ConcreteCMS Vue components, we have to do something like this:

function create() {
    Concrete.Vue.activateContext('cms', function (Vue, config) {
        // Foo
    });
}

What about adding an easier and cleaner way to do that?

async function create() {
    const {Vue, options} = await Concrete.Vue.activateContextAsync('cms');
    // Foo
}