Fix #61700: FILTER_FLAG_IPV6/FILTER_FLAG_NO_PRIV|RES_RANGE failing

It makes no sense to compare IPv6 address ranges as strings; there are
too many different representation possibilities.

Fix #61700: FILTER_FLAG_IPV6/FILTER_FLAG_NO_PRIV|RES_RANGE failing

It makes no sense to compare IPv6 address ranges as strings; there are
too many different representation possibilities. Instead, we change
`_php_filter_validate_ipv6()` so that it can calculate the IP address
as integer array. We do not rely on `inet_pton()` which may not be
available everywhere, at least IPv6 support may not, but rather parse
the IP address manually. Finally, we compare the integers.

Note that this patch does not fix what we consider as reserved and
private, respectively, but merely tries to keep what we had so far.

Co-authored-by: Nikita Popov <nikita.ppv@gmail.com>

Closes GH-7476.

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