- qt5 5.9.7 -> 5.9.9 (skipping some more modules)
- qscintilla 2.11.2 -> 2.11.6
- gettext 0.19.8 -> 0.21 (dropping patch)
- boost 1.65.1 -> 1.74.0
- cgal 4.13 -> 4.14.3
- poppler 21.01.0
- pixman 0.40.0
- cairo 1.16.0

Fix uncaught exception from boost::fs

The do_export() function wants to switch to the parent directory of
the .scad source file for .ast and .csg output. But the path to that
directory is computed at the wrong place, when a different directory
is the current one. This causes failure when the source file is
specified by relative path.

Fixes #3579

Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>

Pre-filter empty geometries before union to avoid unnecessary conversion to Nef when only one non-empty child exists.

Change CGAL_Nef_polyhedron::p3 to hold shared_ptr<const CGAL_Nef_Polyhedron3>, to avoid cache corruption.
Copy constructor just shallow copies for efficiency, and modifying functions require a shared_ptr reset to a new object.

This reverts commit a7bd57c4.