Add FLIP Solver for quick water simulation

[PavelBlend]

@yuanming-hu Hello.

I was trying to create a water simulation using MPM solver. I've noticed that MPM requires a huge number of substeps (hundreds of substeps.). Because of this, the miscalculation takes a very long time. I want to create a water simulation that has 10 million particles. Or maybe with 100 million. Can you add FLIP Solver support (it requires 1 to 20 substeps)? Or maybe another simulation method that is faster than FLIP.

The main thing is that the simulator is very fast and allows you to create 10-100 particle sillions in a reasonable time. And for the domain to be sparse.