Blender Git Loki

Fix for [#23872] particle deflection in conjunction with SPH particles is apparently buggy
* Fix turned into a thorough cleanup and reorganization of particle collision response code.
* Collisions are now much more accurate, stable and even a bit more in agreement with real world physics.
* Only still remaining problem is rotating/deforming deflector objects, but that's something for the future.
* Visible changes should only be positive, i.e. no leaking particles, no strange instabilities etc.