Switch to using expand for scene reductions

[aprokop]

Right now, we do a combination of += and expand in our reduction. I would like to switch to only using expand in order to make the geometric algorithms a general as possible. += relies on internal implementation, while expand() tells us exactly what operations a, say, Box geometry is required to provide.

The goal here is to move all stuff from inside the geometry classes (this includes KDOP and Ray, too) into generic algorithms.

• Deprecate reduction_identity in ArborX::Box and ArborX::ExperimentalHyperGeometry::Box (not sure why we didn't have one in KDOP)
• Deprecate += in ArborX::Box
• Remove += in ArborX::ExperimentalHyperGeometry::Box
• Switch scene calculation to using functors with join operation using expand
• Provide a generic implementation of expand(Box, Point) and expand(Box, Box)

Note that I didn't have to change tstCompileOnlyTypeRequirement.cpp test.

Next step would be redoing KDOP geometry in #982 to include dimension and coordinate, and reorganize it so that there are no internal class functions.

[masterleinad]

I'm in favor of avoiding using operator+= and Kokkos::Sum.

[aprokop]

CUDA builds did not start (failed to check out the source). SYCL timed out. That's ok. Merging.