OpenSystemsDevelopment / qpdf

Some of the images were supposed to have no filter, but somewhere
along the line, they ended up with /FlateDecode, most likely because
qpdf rewrote the file without having --compress-streams=n specified.
If this error is repeated, it will cause a test failure.

Instead of calling assert for problems found during checking
linearization data, throw an exception which is later caught and
issued as an error. Ideally we would handle errors more robustly, but
this is still a significant improvement.

On certain operations, such as iterating through all objects and
adding new indirect objects, walk through the entire object structure
and explicitly resolve any indirect references to non-existent
objects. That prevents new objects from springing into existence and
causing the previously dangling references to point to them.

Create a new need-appearances.pdf based on newer test files with more
modified fields.

Also add some additional methods for detecting form field types to
assist in the json creation and for later use.

Thanks to @p-cher for supplying a patch.

Instead of directly putting the contents of the annotation appearance
streams into the page's content stream, add commands to render the
form xobjects directly. This is a more robust way to do it than the
original solution as it works properly with patterns and avoids
problems with resource name clashes between the pages and the form
xobjects.

Flatten annotations by integrating their appearance streams into the
content stream of the containing page. In the case of form fields,
only flatten if /NeedAppearance is false (or equivalently absent). If
flattening form fields, also remove /AcroForm from the document
catalog.

Generate page content fragment for rendering appearance streams
including all matrix calculation.

Unparse is admittedly strange, but I'd rather be strange and
consistent, and everything else in the qpdf library uses unparse to
serialize. (If you're reading this, the convention of using "unparse"
comes from the "clu" programming language.)

When @file is used and file doesn't exist, just treat it as a normal
argument.