Shading Modes: Material and Render Preview

This change implements the basics as described in {T68312} for the
shading modes.

* LookDev shading mode is renamed to Material Preview. It always uses Eevee as renderer, and is intended to provide a fast material preview suitable for texture painting, and texture and material setup.

* Rendered shading gains "Use Scene Lights" and "Use Scene World" options similar to current Material Preview. These will be enabled by default. When Use Scene World is turned off, HDRIs will be used for lighting instead. These options are available for EEVEE and Cycles.
* Renderers will be able to customize the shading settings panel and add additional settings.

Reviewed By: brecht, fclem

Differential Revision: https://developer.blender.org/D5612

intern/cycles/blender/blender_session.cpp

@@ -861,7 +861,7 @@ void BlenderSession::synchronize(BL::Depsgraph &b_depsgraph_)
 
   /* copy recalc flags, outside of mutex so we can decide to do the real
    * synchronization at a later time to not block on running updates */
-  sync->sync_recalc(b_depsgraph_);
+  sync->sync_recalc(b_depsgraph_, b_v3d);
 
   /* don't do synchronization if on pause */
   if (session_pause) {