Main idea is to make specific engine types be a subclass of generic
ObjectEngineData structure.
This required following changes:
- Have extra size argument to engine data allocation function.
Not sure whether there is less error-prone way of doing this.
- Add init() callback to engine data allocation function.
Additionally, added some extra checks to Eevee's engine data getters, so we do
not silently cast lamp data to lightprobe data.
Reviewers: dfelinto, fclem
Differential Revision: https://developer.blender.org/D3027
006c66b1ff