Make IPv6-embedded IPv4 addresses parse only if they have 4 parts

The URL standard requires the IPv6-embedded IPv4 address to be consicely
composed of 4 parts. A check is added in the URL host parser to fix the
WPT test failures.
The feature is implemented behind the StrictIPv6EmbeddedIPv4AddressParsing flag.

Bug: 1411619
Change-Id: I9062aef7279b899db961613b6e42f6095d2101d1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4206417
Reviewed-by: Tommy Li <tommycli@chromium.org>
Reviewed-by: Charlie Harrison <csharrison@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Jiacheng Guo <gjc@google.com>
Reviewed-by: Weizhong Xia <weizhong@google.com>
Cr-Commit-Position: refs/heads/main@{#1106646}