OpenSystemsDevelopment / qpdf

Per user suggestion in issue 351.

This change works around STL problems with Embarcadero C++ Builder
version 10.2, but std::vector is more common than std::list in qpdf,
and this is a relatively new API, so an API change is tolerable.

Thanks to Thorsten Schöning <6223655+ams-tschoening@users.noreply.github.com>
for the fix.

This also reverts the addition of a new checkLinearization that
distinguishes errors from warnings. There's no practical distinction
between what was considered an error and what was considered a
warning.

Remove dependency on the behavior of perl for reliable creation of
Unicode file names on Windows.

Also add test cases for additional coverage on image optimization.