[RFE] Support OpenEXR 3 / Imath 3

[hobbes1069]

As of OpenEXR 3 upstream has significantly reorganized the libraries including splitting out imath as a standalone library (which this project may or may not need).

Please see: https://github.com/AcademySoftwareFoundation/Imath/blob/master/docs/PortingGuide2-3.md for porting details.

Freeimage and OpenImageIO both build with 3.0 so I would rather not downgrade the whole stack to 2.5.x for LuxCoreRender in Fedora.