This replaces the single-threaded calculation of mesh min and max
positions with a `parallel_reduce` loop. Since the bounding box
of a mesh is retrieved quite often (at the end of each evaluation,
currently 2(?!) times when leaving edit mode, etc.), this makes for a
quite noticeable speedup actually.
On my Ryzen 3700x and a 4.2 million vertex mesh, I observed
a 4.4x performance increase, from 14 ms to 4.4 ms.
I added some methods to `float3` so they would be inlined, but
they're also a nice addition, since they're used often anyway.
Differential Revision: https://developer.blender.org/D13572
6a71b2af66