net: `WriteMsgUDPAddrPort` should accept IPv4-mapped IPv6 destination addresses on IPv4 UDP sockets [1.23 backport]

[gopherbot]

@database64128 requested issue #74737 to be considered for backport to the next 1.23 minor release.

@gopherbot please open backport issues.

In favor of backport:

1. The fix is simple and does not affect the path where it previously worked.
2. net: WriteMsgUDPAddrPort should accept IPv4 destination addresses on IPv6 UDP sockets #52264 had a backport. Backporting this would ensure consistent behavior across both address families.
3. Having a failure mode like this makes WriteMsgUDPAddrPort harder to use right. The problem was discovered by a user under an unusual configuration. Having it backported would eliminate such edge cases that tend to be overlooked.

In opposition:

1. Because net: WriteMsgUDPAddrPort should accept IPv4 destination addresses on IPv6 UDP sockets #52264 was fixed, this issue can be worked around by unmapping the destination address before calling WriteMsgUDPAddrPort.