Take version in gitlab-ci from POM

More versions put into vars in pom.xml
Add debug log to stylesheet manager

Refs #29421

Cf. #24099

HttpUrlConnection by default sets an Accept header that includes HTML
which causes the TextGridRep frontend to display a landing page instead
of delivering the data. We now explicitely request XSLT there.

Fixes #24099

Refs #24099

Cf. #22310

Refs #22310

Refs #22310

Refs #22310

In Java 8, the built-in XSLTC produces invalid XML (containing a
namespace binding to the prefix `xmlns`, cf. #16730). Saxon however
cannot write to a StAXResult, so we need an adapter to SAXResult.

Fixes #16730.

TODO associated stylesheet is detected as a side effect of fetching the
source. Need to make sure this has been done when we call
getTransformer(). We also need a test here.

Refs #14397

Fixes #14397