added property cameraSpaceLightingDef to DirectionalLight

[abmajith]

This property to use in sphere primitive to make the lighting angle constant from view point

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[t20100]

This breaks the lighting of some items.

With python examples/plot3dSceneWindow.py, no items should be black:

[t20100]

This is the cause of the lighting issue with spheres:

silx/src/silx/gui/plot3d/scene/primitives.py

Lines 1743 to 1746 in 51a3827

	/*Lighting performed in NDC*/
	/*TODO update this when lighting changed*/
	//XXX vec3 position = vPosition + vViewRadius * normal;
	gl_FragColor = $lightingCall(vColor, vPosition, normal);

[t20100]

I made PR #4491 to fix this issue