fix CSE evaluation
fix CSE evaluation

Summary:
Use bilinear interpolation, not nearest neighbor interpolation when preparing data for evaluation.

Nits:
 - rename `idxs` to `pixel_vertex_indices`
 - call `argmin(dim=1)` instead of `min(1)[1]`

Reviewed By: MarcSzafraniec

Differential Revision: D25492960

fbshipit-source-id: b8379b893c3ecd4856ab75148352fed62e81fbb9

facebookresearch/detectron2,facebookresearch/detectron2,facebookresearch/detectron2