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.

This hasn't worked or been exercised in years since Adobe stopped
releasing a Linux version of reader.

When linearizing a file or getting the list of all pages in a file,
detect if the pages tree contains a duplicated page object and, if so,
shallow copy it. This makes it possible to have a one to one mapping
of page positions to page objects.