graphics/ilmbase, graphics/openexr: upgrade to upstream v2.4.0
graphics/gstreamer1-plugins-openexr: switch from C++98 to C++11 to
match new OpenEXR headers and unbreak compilation.
Bump PORTREVISION of all ports depending directly on either, based
on assessing INDEX-12 (bump_portrevision.pl -l (shallow) used).
Release Notes:
https://github.com/AcademySoftwareFoundation/openexr/releases/tag/v2.4.0
The update was deliberately deferred until after 2020Q1, and should
not be MFH'd back to it.