Add percentage closer filtering to shadowmap sampling and a
`shadow_filter_radius` property to lights to control it.
Notes:
* This adds PCF to `eevee_shadow_tracing_lib`, but not to
`eevee_shadow_lib`, which is used by volumes (not required) and
thickness.
* PCF is computed based on the LOD0 size. This assumes that higher
LODs are only used when the shadowmap resolution is actually good
enough to match the render resolution.
Pull Request: https://projects.blender.org/blender/blender/pulls/118220
4083f8004d