Clean up the patches / redo them.

This package has known vulnerabilities, please investigate and fix if possible:
 CVE-2021-45844, CVE-2021-45845

Some mods are installed under "${PREFIX}/Mod/", some under "${PREFIX}/share/Mod/".
Should these be moved? E.g. "${PREFIX}/freecad/Mod/"?

Requires the following pkgsrc buildlink3.mk patch to build:

diff --git a/x11/qt6-qtbase/buildlink3.mk b/x11/qt6-qtbase/buildlink3.mk
index 30b7a1562e52..64414308d6ee 100644
--- a/x11/qt6-qtbase/buildlink3.mk
+++ b/x11/qt6-qtbase/buildlink3.mk
@@ -13,6 +13,9 @@ BUILDLINK_INCDIRS.qt6-qtbase+=	qt6/include
 BUILDLINK_LIBDIRS.qt6-qtbase+=	qt6/lib
 BUILDLINK_LIBDIRS.qt6-qtbase+=	qt6/plugins
 
+BUILDLINK_FILES.qt6-qtbase+=	qt6/bin/*
+BUILDLINK_FILES.qt6-qtbase+=	qt6/libexec/*
+
 # \todo Fix duplication with prefix coded in Makefile.common
 QTDIR=		${BUILDLINK_PREFIX.qt6-qtbase}/qt6
 CMAKE_PREFIX_PATH+=	${QTDIR}
