Reshaping to support BSR and GCXS

[willow-ahrens]

After several discussions in the meetings, here's my attempt at adding some reshaping operators to support things like BSR. I've opted not to use a generic list of operations, instead choosing a specific application order. I wish we could have used strides, but there's no easy way to determine if they are well-formed. Instead, I chose to do a split-dimensions then combine-dimensions approach, which ensures that the reshapes always corresponds to bundling or un-bundling underlying dimensions that might have been raveled into the format. I also added a slice keyword at the end to handle padding, and because people asked for slicing.

[github-actions]

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