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

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

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