Improve Skeletal Mesh rendering

[kirides]

E.g. by introducing indexed drawing where applicable.

Something like drawing 50 orc warriors/goblins, lurkers, warans, blood flys, wolves,... should incur a lot less performance hit than drawing 50 different NPCs with different armors, scale, color, ...

We should be able to use Indexed drawing and batching for the main skeletal mesh(es) and SRVs/StructuredBuffers to upload all mesh data, like Bone Transforms per Index, Fatness/Color/World Position data, etc.
We could also check if we can pre-load all used textures (for skeletals) into a "global" texture atlas (Texture2DArray), thus completely remove the need to load them on a case-by-case.

Currently the most inefficient usage of this is drawing the Shadow Map/Cascades which draw each and every skeletal mesh in proximity.

[kirides]

Actually, node attachments are ~90% of the draw calls for skeletals, due to MOBs and things like weapons and heads.

So, to simplify this, we can introduce simple instancing, but for that we need to be able to correctly identify "the same" mesh.

Just this should speed up everything quite enough while keeping CPU usage manageable.