OpenSystemsDevelopment / qpdf

For greater visibility and community participation, track ABI change
ideas that aren't in the source in a github discussion item rather
than in TODO.

Expose functions to the C API to create new loggers and to setLogger
and getLogger for QPDF and QPDFJob.

QPDFValueProxy wasn't a good name for it. We decided the evil of
having the header file be named QPDFObject_private.hh was less than
the evil of having the class be named something other than what it
should have been named.

I decided that it's actually fine to copy a direct object to another
QPDF. Even if we eventually prevent a QPDFObject from having multiple
parents, this could happen if an object is moved.

When a QPDF is destroyed, changing indirect objects to direct nulls
makes them effectively disappear silently when they sneak into other
places. Instead, we should treat this as an error. Adding a destroyed
object type makes this possible.

It might be worth enabling code scanning at GitHub, which is a
superset of lgtm.

A bug was fixed between qpdf 8.4.2 and 9.0.0 regarding this type of
file (see #305 and #311), but it was necessary to retest after some
major refactoring work at the lexical and parsing layers. This lays
the groundwork for including this in performance benchmarks and in the
qpdf test suite rather than having to keep a large,
non-redistributable file around.

20 arrays of 20K nulls is plenty for performance memory testing and
doesn't take too long to run. Compared to qpdf 8.4.2, in qpdf 11.0.0,
the file generated here uses 3% of the RAM and runs over 4 times
faster.

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.

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.