New HTMLForm size filter field; add size filter to Special:Newpages

New HTMLForm size filter field; add size filter to Special:Newpages

The conversion of SpecialNewpages to HTMLForm seems to be half-finished.
It's not using HTMLForm to read in the request query, which means we have
to roll our own logic. Kind of defeats the purpose of using HTMLForm in
the first place.

When ProtectedPages is converted to HTMLForm (T117722), it can use this new
field type.

Bug: T12817
Change-Id: I069609fbb37b18c3df25156779ad7ac7cd5d6813