Blender Matcap Shader

Based on Blender's workbench matcap shading

https://github.com/dfelinto/blender/blob/f5e0ae655e5182de3ee9cfedfbdc2a20f9b047fb/source/blender/draw/engines/workbench/shaders/workbench_common_lib.glsl#129

Change log:

• v1: initial upload
• v2: fixed orthographic view, exposed normal socket to allow custom normal maps to be used