[3.12] gh-87799: Improve the textual representation of IPv4-mapped IPv6 addresses (GH-29345) (GH-135081)

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).

(cherry picked from commit f22bf8e3cf899896cf587099d29290cb43aa9724)

Co-authored-by: opavliuk <40970635+opavlyuk@users.noreply.github.com>
Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
Co-authored-by: Andrew Svetlov <andrew.svetlov@gmail.com>