[SpriteEffects] The refraction shader should preferably use register(s1)

[rbwhitaker]

In refraction.fx, the original code used this:

sampler DisplacementSampler : register(s1);

The code used this:

graphics.GraphicsDevice.Textures[1] = waterfallTexture;

That would be the ideal solution, but it is unclear if MonoGame can support this. (Possibly on the DirectX side?)

The temporary solution works well enough: use a shader parameter instead, which required defining a new texture and sampler and setting those with a Parameters[x].SetValue(texture).

If we can make it work the original way, that would be better.