cad/openvsp: update to 3.39.0

ChangeLog: https://github.com/OpenVSP/OpenVSP/releases/tag/OpenVSP_3.39.0

Features:

• 3D Background images

Library Updates:

• Update to latest FLTK dev as they approach 1.4.0
• Build LibXml2 with -PIC
• Update GLEW build integration to match modern GLEW

Bug Fixes:

• Move Documentation build to MacOS from Ubuntu to get latest Swig
• Drop MacOS-11 build, move to MacOS-12
• Use gcc-11 on MacOS for ADEPT and OMP builds
• Fix MeshGeom DrawObj issue
• Tighten tolerance in MatchBorderNodes