Blender Git Loki

Viewport: MSAA support during ViewportRendering

When rendering viewport to an offscreen buffer the buffer was
constructed for non anti aliasing (0 samples). This made the objects
that are drawn by the `object_mode` including `wireframe` draw type
non-anti-aliased.

The offscreen buffers will be constructed based on the user setting for
viewport multisampling (`U.ogl_multisamples`). The same setting will
also be used when previewing scene strips in the sequencer. For now
this only improves wireframe drawing in the scene strips. To improve the
Anti aliasing in the scene strips we need to get finer control in the
draw manager. This will be part of a different patch I am preparing.

Please note that this patch also cleansup some unused code in the offscreen rendering (FSAA code was still existing, but never called)

Reviewed By: brecht

Maniphest Tasks: T64849

Differential Revision: https://developer.blender.org/D4907