Fix Cycles to mostly work with render layer / depsgraph changes.

Point density texture and motion blur are still broken, and many more changes
are needed in general to used evaluated datablocks.

Use lean/shallow EvaluationContext for point density texture

I'm confident this is not working, but I want to check with others how to test
this and if we need a full EvaluationContext with depsgraph for this.

Merge remote-tracking branch 'origin/blender2.8' into temp-render-depsgraph

Fix Sequencer for new depsgraph/render changes

From review: render_to_image should not get RenderLayer

Move render ViewLayer iterator outside render_result_new

From review: Move depsgraph away from render layer and change render loop

Create depsgraph as part of the render loop and pass a render layer for the
render_to_image. Optionally we could create a single layered render_result
but why would we?

Depsgraph is created from scratch prior to rendering each frame.
So I got rid of most of the partial update calls we had during the render
pipeline.

Also, it's past the time to remove Blender Internal.

Note 1: Cycles doesn't build.

Note 2: Cycles seems to rely on an "empty" render function, where all the
required settings are passed to the update function instead. I would like
to have this cleared out because draw manager is assuming everything is
passed to render_to_image, but we need to have an API that makes sense
to all cases.

Merge remote-tracking branch 'origin/blender2.8' into temp-render-depsgraph

Merge remote-tracking branch 'origin/blender2.8' into temp-render-depsgraph

Depsgraph: Expose query to get view layer to RNA

Merge remote-tracking branch 'origin/blender2.8' into temp-render-depsgraph

Cleanup: Always have viewlayer when updating scene graph

From review: Avoid chicken-egg situation with EvaluationContext/Depsgraph

From review: Add compreensible comments on Cycles

From review: Initialize struct based on struct elements declaration order

From review, depsgraph should always be valid for render layers

Move render depsgraph to where it belongs: RenderLayer

This fixes compositing for Eevee as well as lay the ground work to fix Cycles
objects iteration in blender 2.8.

Note: Work in progress, the following is not working:
* Cycles
** see "#ifdef TODO" in blender_session.cpp

* Sequencer
** pipeline.c calls BKE_sequencer_new_render_data() early on, and assumes an eval_ctx from that moment on

* Point cache texture (RE_sample_material_init)
** needs eval_ctx :/

What is not handled here: Get rid of view layer in EvaluationContext.
We should store ViewLayer in RenderLayer. The patch is massive as it is though.

Update depsgraph before drawing the render layers

* Store the required depsgraph and eval_ctx in the render layers
* Call BKE_scene_graph_update_tagged() for these depsgraphs.

Reviewers: sergey

Subscribers: fclem

Differential Revision: https://developer.blender.org/D3073

Store the required depsgraph and eval_ctx in the render layers

Missing: To call the equivalent of BKE_scene_graph_update_tagged() for these depsgraphs.

From review: Don't touch re->eval_ctx here

This could go away even, but we are still using it in a few parts.