[models] Built-in 3D models are missing vertex normals

[fasterik]

While experimenting with the 3D API and shaders, I discovered that my lighting only works with DrawCube and DrawPlane. Doing a Ctrl+F in rmodels.c confirms that these are the only only functions in that file that call rlNormal3f. It appears that other 3D primitives will reuse the last normal output by a previous draw call. I believe the following functions need to be modified to output vertex normals:

• DrawCircle3D
• DrawTriangle3D
• DrawTriangleStrip3D
• DrawSphereEx
• DrawCylinder
• DrawCylinderEx
• DrawCapsule