mounting options: slots/scoped slots

[lmiller1990]

Slots are a pain point in VTU beta. We should make sure there are tests for all the cases, and they all work as expected.

Ref: slots specs in VTU beta: https://github.com/vuejs/vue-test-utils/blob/dev/test/specs/mounting-options/slots.spec.js

We should port the ones that are relevant to this codebase.

NOTE: slots and scoped slots are now the same thing in Vue 3.

[lmiller1990]

We have basic support:

https://vuejs.github.io/vue-test-utils-next-docs/api/#slots

We should support { template: "<div />" } as well. I could not get this working but I will try again soon.

[lmiller1990]

@dobromir-hristov is there anything else we need to look into for slots? I believe you made a PR around this already.

[dobromir-hristov]

Yeah, helpers at most.