devel/libqb: Improve the port
- Add EXAMPLES option
- Add support for activation of tests (still failing)
- Fix conditional BUILD_DEPENDS on libxml2 for doxygen2man
- Fix a typo
PR: 282536
MFH: 2024Q4
(cherry picked from commit 7945736569ee6db4563ff713a70a5876d9c5d836)