Consider splitting up shadow shaders to eliminate excess branching.

[bryanedds]

Right now we just have a single shadow shader for each surface type with a switch statement to vary behavior depending on the light type whose shadow is being rendered. We should probably go ahead and split each case up into its own set of shadow shaders.

[bryanedds]

There might be pretty limited benefit to doing so since lightType comes in on a uniform, so the switch cases are probably eliminated at raster time.

[bryanedds]

Now that we're using PCF in point lights, we only need one channel there, so we could halve the size of the shadow map if we split the shaders.