The issue would happened in any situation where the light
moves (update, animation, jitter) or have a lot of LOD
tagged by moving casters. In these cases, the actual
effective LOD min is bigger than the one from the UI which
results in shadow acnee artifacts (because the computed bias
is too small).
This patch saves the effective min LOD per tilemaps and
amend the `light.lod_min` to replace it by the min of
all tilemaps in used by one light.
6ce4e94eb9