[Pass request] Fuse Pad - Pooling (Avg/MaxPool)

[phager90]

This is not an issue but a feature request for adding a fuse_pad_into_pool optimizer pass.

Currently, 'nop' pad layer are removed by eliminate_nop_pad.
Also, pad layers before conv layers are fused by fuse_pad_into_conv.

It would be desirable to have the same behavior also for pooling layers (AveragePool, MaxPool):
i.e.: fusing pad layers before pool layers into the pool layer.

Aka adding a fuse_pad_into_pool optimizer pass.

If you prefer us to provide a pull request for this feature, let us know.