OpenSystemsDevelopment / qpdf

Various PDF digital signing tools do not encrypt /Contents value in
signature dictionary. Adobe Acrobat Reader DC can handle a PDF with
the /Contents value not encrypted.

Write Contents in signature dictionary without encryption

Tests ensure that string /Contents are not handled specially when not
found in sig dicts.

Table 8.93 "Entries in a signature dictionary" in PDF 1.5 reference
describes that the value of Contents entry is a hexadecimal string
representation when ByteRange is specified.

This commit makes QPDF always uses hexadecimal strings representation
instead of literal strings for it.

Use destructors to pop the pipeline stack, and ensure that code that
pops the stack is actually popping the intended thing.

Just because we know an indirect reference is null, doesn't mean we
shouldn't keep it indirect.

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.

Use PointerHolder in several places where manually memory allocation
and deallocation were being used. This helps to protect against memory
leaks when exceptions are thrown in surprising places.

This code was essentially duplicated between test_driver and
standalone_fuzz_target_runner.

In a small number of cases, it makes sense to replace an overloaded
function with a function that takes a default argument. We can do this
now because we've already broken binary compatibility since the last
release.

Have classes contain only a single private member of type
PointerHolder<Members>. This makes it safe to change the structure of
the Members class without breaking binary compatibility. Many of the
classes already follow this pattern quite successfully. This brings in
the rest of the class that are part of the public API.

This makes all integer type conversions that have potential data loss
explicit with calls that do range checks and raise an exception. After
this commit, qpdf builds with no warnings when -Wsign-conversion
-Wconversion is used with gcc or clang or when -W3 -Wd4800 is used
with MSVC. This significantly reduces the likelihood of potential
crashes from bogus integer values.

There are some parts of the code that take int when they should take
size_t or an offset. Such places would make qpdf not support files
with more than 2^31 of something that usually wouldn't be so large. In
the event that such a file shows up and is valid, at least qpdf would
raise an error in the right spot so the issue could be legitimately
addressed rather than failing in some weird way because of a silent
overflow condition.

This is the type we need for the underlying zlib implementation.

Change from unsigned long to int since we pass enumerated type values
to this field.