[6.x] Fix exclude validation rules for nested data

[SjorsO]

PR #30835 added the exclude_if and exclude_unless validation rules. The following example currently doesn't work, this PR fixes that:

$request->validate([
    'vehicles.*.type' => 'required|in:car,boat',
    'vehicles.*.wheels' => 'exclude_if:vehicles.*.type,boat|required|numeric',
]);

---

The tests in this PR also contains an example of fields nested 2 levels deep getting included in the validated data, even though they don't have a validation rule. There has been discussion about this bug/feature in the past: laravel/ideas#1993 (comment). This is unrelated to the exclude validation rules, but I ran into it and thought it would be a useful addition to the test suite.

---

This PR came from trying to replicate the weird behavior I encountered while making the original PR (see: #30835 (comment)). I couldn't replicate it, I must have been doing something wrong.