Qt5: Update to 5.15.16
Update devel/pyside2* and devel/shiboken2 to 5.15.16
Update www/qt5-webengine to include the latest security fixes in
the chromium submodule [1]
Release note:
https://code.qt.io/cgit/qt/qtreleasenotes.git/about/qt/5.15.16/release-note.md
MFH: 2024Q4
Security: 16e472d5-a8aa-11ef-b680-4ccc6adda413 [1]