A protected field is not accessible unless we are referencing it from within a
class which extends its owner. Therefore, we may use a synthetic property with
the same name as long as we do not have access to the field.

When we used to remap `a.pkg.A.Inner` we would apply both mappings (the one for
the inner class and the one for the outer class) at the same time, resulting in
`b.pkg.B.Inner.Inner`.
The direct cause being that we only checked conflicts for the range of the
respective expression (which is just `A` and `Inner` for Kotlin, and therefore
not conflicting) instead of the parent as we should have.

With that fixed, it now also becomes apparent that we need to apply mappings for
dot qualified expressions back to front (otherwise the outer class takes
priority), so that is the second thing this commit change.

To ensure the mixin target is being remapped, even though the corresponding
PsiClass cannot be found.