Blender Git Loki

Fix T46641: Bicubic transform on ID channel is not bicubic

Better support of bicubic sampling of ID mask output.

The idea is to generate ID mask into a temporary buffer which is then being
interpolated using current sampling method.

This works fine for upscaling or rotating the ID mask but does not work for
scaling down. This is much-much bigger problem of the compositor design and
can't really be solved currently. Same will happen with other nodes like
blur for example.

Reviewers: campbellbarton

Subscribers: ania

Differential Revision: https://developer.blender.org/D1612