the rank of `input`. For each dimension D of `input`, `paddings[D, 0]`
    indicates how many zeros to add before the contents of `input` in that
    dimension, and `paddings[D, 1]` indicates how many zeros to add after the
    contents of `input` in that dimension.

    The padded size of each dimension D of the output is:

      `paddings(D, 0) + input.dim_size(D) + paddings(D, 1)`