Parsing last as an IPV4 number was not returning true in "ends with a
number" as the parsing of that part was overflowing. This means that the
URL is not considered to be an IPv4 address, and is treated as a valid
domain.
Helpfully, the spec also points out in a note that this step is
equivalent to simply checking that the last part ends with 0x followed
by only hex digits - which doesn't suffer from any overflow problem!
Arguably this is an editorial issue in the spec where this should be
clarified a little bit. But for now, fixing this fixes 3 sub tests in
WPT for:
https://wpt.live/url/url-constructor.any.html
Our heuristic was a bit too simplistic and would not run through the
ToASCII unicode algorithm which performs some extra validation. This
would cause invalid URLs that should fail to be parsed be mistakenly
accepted.
This fixes 8 tests in: https://wpt.live/url/url-constructor.any.html
