Summary: Performance improvement: Use torch.lerp to map uv coordinates to the range needed for grid_sample (i.e. map [0, 1] to [-1, 1] and invert the y-axis)

Reviewed By: bottler

Differential Revision: D51961728

fbshipit-source-id: db19a5e3f482e9af7b96b20f88a1e5d0076dac43