fix: do not include self when using findAll

[lmiller1990]

resolves #1233

Seems too easy 🤔

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[lmiller1990]

cc @freakzlike @aethr WDYT?

[cexbrayat]

LGTM

[xanf]

👀 Looking on this right now

[xanf]

@lmiller1990 This breaks the logic we've discussed in #1233

    expect(wrapper.findAll('div').length).toBe(4) // actually returns 3

Let's keep this discussion in #1233 (comment) to keep all the context in one place

[lmiller1990]

@xanf pushed a commit to fix that.

[xanf]

@lmiller1990 looking

[xanf]

@lmiller1990 while reviewing your PR I've found another failing case - https://github.com/vuejs/test-utils/pull/1392/files#diff-9835123bc80f420fd7ebbcc25a72c73e7f2c8934bac14a9a3bbe6e1dca3569f7R356

And I believe I've figured more elegant approach in #1392
Could you please look at that (basically we simply separated implementations of findAll for VueWrapper and DOMWrapper.
Feel free to close that PR is favor of this one if you feel that this approach is better

/cc @cexbrayat