OpenSystemsDevelopment / qpdf

Virtually all changes are merged through PRs now. The exclusions would
prevent a README change from being the last commit before a release.

This requires a special build option.

As of this moment, if a specific commit's coverage data is uploaded to
CodeCov via a pull request, when that exact same commit builds in
main, the branch is not associated with the commit. I'm hoping this
might work around that.

Still need to handle upload artifacts, but that requires additional
changes.

...as well as some cases generated in CI from earlier attempts at
fixing this.

Add a CI job to test qpdf with other than the default zlib
implementation. This incldues a check that the new zlib really is not
the default, so the new test will fail if the default because zlib-ng.

libjpeg development files are on the macos GitHub Actions build image
now, and downloading our own version was causing conflicts.

I run the fuzzer test suite, which should be good enough to avoid
wasting resources on this every time I push to build.

Main branch is `main` now

External libraries for Windows are now built automatically in the
qpdf/external-libs repository and include openssl in addition to zlib
and jpeg. Use these, and update the Windows build to build with the
openssl crypto provider by default. We leave the native crypto
provider enabled in case there is a problem with openssl and also to
continue to exercise that code.

Wildcard expansion is different in Windows from non-Windows and
sometimes requires special link options to work. Add tests that fail
if we link incorrectly.

Preparing to migrate qpdf's main build/CI to GitHub actions