Update Light2D rect_cache even when not using shadows.

[clayjohn]

Fixes: #100922

Regression introduced in #100677

#100677 Updated the rect_cache to be in canvas space instead of light local space. However, it mistakenly only did that when shadows were enabled. So unshadowed lights had the rect_cache in the wrong coordinate space.

The simplest solution would be to just move the line that updates the rect_cache outside the scope of the use_shadow block. However, to avoid this sort of confusion, I have updated how the cache is calculated. Instead of setting it in one coordinate space then updating it, we initialize it in the proper coordinate space and only use the local rect in this code path.

[akien-mga]

Thanks!