OpenSystemsDevelopment / qpdf

Turns out unreadCh is much more efficient than seek(-1, SEEK_CUR).
Update comments and code to reflect this.

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.

Specifically, if a stream had its stream data replaced and had
indirect /Filter or /DecodeParms, it would result in non-silent loss
of data and/or internal error.

There isn't really an issue with these files causing a real problem,
but malware and virus checkers trip on them, and the value to leaving
them in the test suite is too low to be worth the hassle.

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.

This is suitable for use as a Lambda layer in AWS, inclusion in a
docker container, or other places where a minimal binary distribution
is desired.

This is all that ever worked. The test suite was trying to do
something different from ClosedFileInputSource.

It is redundant with qpdf's main CI environment, which is Azure
Pipelines, but may soon be migrated to GitHub Actions.

Make clear that you almost always want + or - before an angle when
specifying rotation.

StreamDataProvider::provideStreamData now has a rich enough API for it
to effectively proxy to pipeStreamData.