t9904: add tests for the new url-parse builtin

t9904: add tests for the new url-parse builtin

Test git URL parsing, validation and component extraction
on all documented git URL schemes and syntaxes.

Add IPv6 host coverage in URL form:

    ssh://[::1]/path
    ssh://user@[::1]:1234/path
    git://[::1]:9418/path
    http://[2001:db8::1]/path
    https://[2001:db8::1]/path

In URL form the brackets are kept in the host component (RFC 3986
syntax for IPv6 literals).

Also exercise the bracketed scp short forms that t5601-clone.sh
covers via parse_connect_url:

    [host]:path
    [host:port]:path
    [::1]:repo
    user@[::1]:repo
    user@[host:port]:path

In scp form, brackets are kept for IPv6 literals (two or more inner
colons) and stripped for plain hostnames or host:port pairs.

Suggested-by: Torsten Bögershausen <tboegi@web.de>
Signed-off-by: Matheus Afonso Martins Moreira <matheus@matheusmoreira.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>