Blender Git Loki

Compositor: Add sampling methods for full frame

Current sampling methods have off by one issues on full frame:
- Bilinear sampling do not fully sample bottom and left image border,
creating edges.
- Single elem buffers are not sampled at all when they should be
at least on the borders to smooth edges.
- EWA filtering is partially implemented on `ReadBufferOperation`, it
needs to be moved to `MemoryBuffer` on full frame.

In order to not affect tiled implementation, this commit creates
specific sampling methods for full frame needs.

Reviewed By: jbakker

Differential Revision: https://developer.blender.org/D12164