Workbench: Shadows

Workbench: Shadows

Initial review of the shard shadows in the workbench engine.

Speed optimizations like transform feedback are not implemented yet. I first want this part to be reviewed and merged.

@fclem please check the note in drw_stencil_set it was holding back nequal == 0 as by default DST.stencil_mask was set to 0. questioin is should we remove the whole check or not.

Also I am still looking for a better name (or split the enum) for DRW_STATE_STENCIL_DEPTH_FAIL_INCR_DECR_WRAP

Reviewers: fclem

Reviewed By: fclem

Tags: #code_quest

Differential Revision: https://developer.blender.org/D3198