Backport #17254 to 20.12: Fix \"Unexpected packet Data received from client\"  for Distributed queries

Sometimes it is odd to get TLD itself from the
cutToFirstSignificantSubdomain() (since you will not get TLD itself if
you pass it directly):
- cutToFirstSignificantSubdomain('org')            -> ""
- cutToFirstSignificantSubdomain('www.org')        -> org
- cutToFirstSignificantSubdomain('kernel.org')     -> kernel.org
- cutToFirstSignificantSubdomain('www.kernel.org') -> kernel.org

So add one more function to get www.org in this case:
- cutToFirstSignificantSubdomainWithWWW('org')            -> ""
- cutToFirstSignificantSubdomainWithWWW('www.org')        -> www.org
- cutToFirstSignificantSubdomainWithWWW('kernel.org')     -> kernel.org
- cutToFirstSignificantSubdomainWithWWW('www.kernel.org') -> kernel.org

P.S. not sure about the naming though, so it will great if someone has
suggestion for the name.

(cherry picked from commit b5a8ef3c)