runtime(sudoers): improve recognized Runas_Spec and Tag_Spec items

runtime(sudoers): improve recognized Runas_Spec and Tag_Spec items

Recognize colon-delimited second part of Runas_Spec that specifies
permitted groups, e.g.:

    alan ALL = (root, bin : operator, system) ALL

This implementation is sloppy because it accepts any amount of colons
delimiting further Runas_Lists, but for now that's better than bailing
out completely as soon as a colon is encountered (esp. given that the
default sudoers uses these colons, breaking highlighting OOTB).

Also, while at it, make Vim recognize all Tag_Spec items, not just
{,NO}PASSWD

closes: #15607

Signed-off-by: Ivan Shapovalov <intelfx@intelfx.name>
Signed-off-by: Eisuke Kawashima <e-kwsm@users.noreply.github.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>