Blender Git Loki

DrawManager: Disable Clipping in material/rendered mode

Viewport: Disable Clipping For EEVEE and External Renderers

Currently it is possible that, when using viewport clipping, the display and tools communicate
different information to the user then the renderer does. The reason is
that the renderer does not support viewport clipping. Both EEVEE and
Cycles do not support it.

This patch will disable the clipping in all the tools and drawing code
when the viewport drawing mode is `Material Preview` or `Rendered`.

This patch introduces a `RV3D_CLIPPING_ENABLED` util that checks if
clipping is enabled for the given `rv3d` and `v3d`. Also in places where
it was needed we added the `ViewContext` as a carrier for the `View3D`
and `RegionView3D`.

There are a few areas in the tooling (select, projection painting) that
still needs to be tackled after this patch.

Reviewed By: fclem

Differential Revision: https://developer.blender.org/D6047