Load cursor from the icon theme similar to how the
gtk VCL plugins do it.
This not only allows using the themed cursor icons,
but also helps avoid QTBUG-95434 [1]
("Bitmap cursors not supported on QtWayland")
that would result in no cursor being shown on Wayland at all
when our custom bitmap cursors are used.
[1] https://bugreports.qt.io/browse/QTBUG-95434
Change-Id: Id65db4e7d71b8cee8a514c06c21c59dcc2afa889
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/147379
Tested-by: Jenkins
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>
