fix: wrapper.element with nested multiple roots

[freakzlike]

fix #1461

wrapper.element did not return the correct element for some edge cases with multiple root nodes.
For example when using another component in template which has multiple root elements:

<template>
  <WithMultipleRoots />
</template>

This has led to issues with wrapper.text() (#1461)

I had to differ between stateful and functional components to avoid other failing tests. Maybe not all edge cases covered.

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[aethr]

Legend! 🥇

[cexbrayat]

LGTM 👍

[lmiller1990]

Nice job figuring this out!