OpenSystemsDevelopment / qpdf

This results in measurable performance improvements to packaged binary
libqpdf distributions. QTC remains available for library users and is
still selectively enabled in CI.

It turns out that QUtil::get_env is particularly expensive on Windows
if there is a large environment. This may be true on other platforms
as well.

This is a guess...I'm not sure exactly why there are linker issues or
how to reproduce them.

Code tidy: remove redundant calls to smart_ptrs get() method

Add QPDF::getObject to replace getObjectByObjGen and getObjectByID

Inline QPDFObjectHandle::getObjGen etc

For consistency with similar methods, e.g. replaceObject.

Also, make QPDFObjectHandle::isIndirect const.

Now --json-output just changes defaults. Allow output file with --json.

from "qpdf-v2" to "qpdf": [..., ...]

Add additional parameters that will be needed to call QPDF::writeJSON
in partial mode.

Code tidy : replace 0 with nullptr or true

Over time, qpdf's grade has dropped on lgtm, but they are not
transparent about how grades are assigned. Fixing current alerts, in
my opinion, reduces clarity and maintainability of the code in the
name of performance in non-critical sections of code. Some analysis by
m-holger suggests that fixing some of the current alerts actually
degrades performance (slightly) while fixing others results in
insignificant improvements. The quality of qpdf can be measured in
other ways, such as its extensive test suite, documentation, and long
track record of reliably manipulating PDFs with high performance, few
bugs, and few external dependencies. The lgtm rating is a distraction
at best.

When the schema wants a variable-length array, allow a single item as
well as allowing an array.

Remove any ambiguity around whether old or new value is being
returned.