Implement Physical Light Units as an optional setting.

This allows light sources to be specified in physical light units in addition to the regular energy multiplier. In order to avoid loss of precision at high values, brightness values are premultiplied by an exposure normalization value.

In support of Physical Light Units this PR also renames CameraEffects to CameraAttributes.

servers/rendering/renderer_rd/shaders/environment/sdfgi_debug.glsl

@@ -21,6 +21,7 @@ struct CascadeData {
 	float to_cell; // 1/bounds * grid_size
 	ivec3 probe_world_offset;
 	uint pad;
+	vec4 pad2;
 };
 
 layout(set = 0, binding = 9, std140) uniform Cascades {