Document jax.lax.padtype_to_pads

[patrick-kidger]

JAX has the jax.lax.padtype_to_pads function for converting string-specified padding e.g. padding='same' into the before-and-after numeric padding.

This seems to be useful for downstream libraries looking to implement their own convolutional layers. In particular this comes up when wanting to (a) duplicate the string-based padding behaviour of lax.conv_general_dilated, but (b) use nonzero padding (e.g. circular padding instead).

Right now it's not documented. Would this be something we can add to the public API?