[1/2] ntdll: Implement RtlIpv4StringToAddressW.

[Thomas Faber]

Hi,

what can I do to get this in committable shape?
I don't see how it can be reasonably split up; tests are in place.

I've noticed I forgot to remove the L prefixes on character constants,
which I'll correct.
I'll gladly fix any other style issues.

The function _could_ be implemented using strto(u)l instead of using
its own conversion function, but that would require the removal of some
tests as "too strict". I much prefer the "correct" version.

Thanks for any input.

Best regards,
Tom