gh-87799: Improve the textual representation of IPv4-mapped IPv6 addresses (#29345)

Represent IPv4-mapped IPv6 address as x:x:x:x:x:x:d.d.d.d,
where the 'x's are the hexadecimal values
of the six high-order 16-bit pieces of the address,
and the 'd's are the decimal values
of the four low-order 8-bit pieces of the address
(standard IPv4 representation).

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Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
Co-authored-by: Andrew Svetlov <andrew.svetlov@gmail.com>