Lights: change sun light size to be specified as angle

This is the angular diameter as seen from earth, which is between 0.526° and
0.545° in reality. Sharing the size with other light types did not make much
sense and meant the unit was unclear.

Differential Revision: https://developer.blender.org/D4819

intern/cycles/blender/blender_object.cpp

@@ -149,7 +149,7 @@ void BlenderSync::sync_light(BL::Object &b_parent,
     // }
     case BL::Light::type_SUN: {
       BL::SunLight b_sun_light(b_light);
-      light->size = b_sun_light.shadow_soft_size();
+      light->angle = b_sun_light.angle();
       light->type = LIGHT_DISTANT;
       break;
     }