rust-url: Properly log validation errors related to legacy IPv4 notations

The current rev of the URL Standard specifies that the various legacy notations accepted by inet_aton for IPv4 addresses are validation errors, but rust-url silently accepts them (they’re not even diagnosed via the syntax violation callback). I would like to have an option to reject these.

Examples of undesirable constructs:

# all are treated as equivalent to http://127.0.0.1/
http://127.0.1/
http://127.1/
http://0177.0.1/
http://0177.0.0.1/
http://0177.1/
http://0x7f.0.1/
http://0x7f.0.0.1/
http://0x7f.1/
http://2130706433/
http://0x7f000001/
http://017700000001/

# equivalent to http://127.0.0.8/ , not http://127.0.0.10/
http://0127.0.0.010/

See https://url.spec.whatwg.org/#concept-ipv4-parser (pay close attention to where it, and its subroutine https://url.spec.whatwg.org/#ipv4-number-parser , set the “validationErrorFlag”) for gory details.

Previous discussion in #116.