Fix two problems arising from 1.21 changes

After Id9cdf102 was merged into core MediaWiki, ApiSandbox started
HTML escaping pretty-printed output that the API already escaped.
To correct this double escaping, I changed the regex to match the
pre element even if it has one or more attributes.

Because interpreting anything that looks like HTML as HTML is quite
scary, I also added a content-type check that should detect most
non-HTML output.

A separate change to the API means that parameters of the pageset
module appear as part of the query module, resulting in a
nonfunctional duplicate set of text boxes. So I removed the two
references to that module (as well as the now-dead branch in
the UiBuilder constructor).

Bug: 45634
Change-Id: I95b7cac5bba8d989f7d95f515711500762718b9e
Merge "Fix two problems arising from 1.21 changes"