Clamp branching factor

[stefanatwork]

Limiting the branching factor of the standalone BVH builder.

[johguenther]

LGTM, just some questions/comments

• the regression test does nowhere check whether children are <=8 (MAX_BRANCHING_FACTOR), so basically without the fix, the builder would crash (stack overflow)? But what if maxBranchingFactor is set to 9 without the fix / clamp, it may not crash (just slightly above the limit), just be corrupt?
• needs un-draft and should be squashed

[johguenther]

actually, embree_regression_morton_builder_clamp already crashes (without modifications)

[johguenther]

• test passes, good
• when I remove the fix (clamp branching in builder), the test segfaults (expected, but a fail would be better)
• when I now reduce test requested branching to 6 via runCase(6), the test still segfaults, bad (segfault is in embree/kernels/common/alloc.h:517 all slotMutex[] are nullptr, called by morton_builder_clamp_regression.cpp:createLeaf()->rtcThreadLocalAlloc())

I'd recommend to replace the asserts by std::throw and remove all other code which allocates or writes to memory. This way the regression test does not depend on asserts being compiled and the thrown exception (in case of a regression) is handled by the test framework (then failing properly instead of crashing -- at least not crashing in the test, but maybe in the builder).

the new file morton_builder_clamp_regression.cpp still needs clang-formated

[svenwoop]

The internal builders should fail when invalid config is passed, as this is really an error when we want to use wide BVHs. This which is also how this is handled in some other builders. The BVH builder API could clamp max width to 8, which is supported by all builders.

kernels/builders/bvh_builder_msmblur.h already fails (ok)
kernels/builders/bvh_builder_sah.h fails already fails (ok)
kernels/builders/bvh_builder_msmblur_hair.h should also fail
kernels/builders/bvh_builder_hair.h should also fail!
kernels/builders/bvh_builder_morton.h should fail!

[svenwoop]

see last comment