Add support to invade Testable

[PerryvanderMeer]

Every now and then I involve private and protected functions and properties in my tests.
It can be challenging to access those while testing, although invade() is the ideal solution.

This PR adds support for accessing protected and private functions and properties while testing via ->invade().

$component = Livewire::test(new class extends Component {
    protected string $foo = 'bar';
});

$component->invade()->foo; // bar

I have this by default in my projects via a Mixin, but it may be useful to others as well.

[calebporzio]

This is pretty cool!