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
Use the term "AFTER" instead of "OFS" since it wasn't obvious these
macros operate on everything after the struct member passed.
Avoid casting to non-const types when only reading.