Allocate sunlight shadow maps to fixed area of shadow map

[no-lex]

As the Imprimis engine will be designed largely for sunlit maps, having the sunlight be a key part of the shadow atlas rather than as an equal member compared to light entities is a logical consequence.

By setting the CSM size to take up three quarters of the total shadow atlas (2048) and then affixing them to set locations in the shadow atlas, it should be possible to alleviate many of the shadow map aliasing problems that come with large sunlight SMs.