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.

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

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.

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.

Also, change test for QPDFObjGen::isIndirect to obj != 0.
Delete comment from commit afd35f9.

Use 'QPDFObjGen const&' instead of 'int, int' in signature.

Change method signatures to use QPDFObjGen.
Use QPDFObjGen methods where possible.
Remove redundant QPDF::objGenToIndirect.

Change method signature to use QPDFObjGen.

Change method signature to use QPDFObjGen.

Also, revert inlining of unparse and operator << from commit 4c6640c in
order to avoid exposing QUtil.

ABI breaking change

Move responsibility for creating shared pointers to objects and cloning from QPDFObjectHandle to QPDFObject.