match IPv4MappedToIPv6 address in IPv4 networks

[wfurt]

fixes #98427.
This change does exactly what #98427 asked for. e.g. if there IPv4 IPNetwork Pv4-Mapped IPv6 Addresses address would function same as it's IPv4 equivalent. This prevents hassle and allocations from IPAddress.MapToIPv4 one would have to use.

Note that this is not symmetric. e.g. if somebody would create IPNetwork with ::ffff:192.168.0.0/24 IPv4 address would not match that at the moment. We can fix that if we want to @MihaZupan and @antonfirsov. But I;'m not sure if there is compelling use case. (I can see one for the address from DualMode Socket)

[MihuBot]

Thanks.
I agree this should be the more common direction (IPv4 IPNetwork + DualMode addresses to test).

[MihaZupan]

Oops :)