* Changed `MeshSharding::sharded_dims_sizes` from representing sizes per
shard to offsets to origin per shard.
- Local shard size are now a simple subtraction
- Offsets are now readily available without a reduction operation
- Enables constant value/shape propagation through standard
canonicalization
- Renamed to `sharded_dims_offsets` accordingly.
* First spmdization pattern for halo regions.
- Triggers when source and destination shardings differ only in their
halo sizes
- Copies local data from source into a new tensor and calls update_halo
- Supports arbitrary mesh dimensions (unlike the other patterns which
work on 1d meshes only)
* `UpdateHaloOp` implements `DestinationStyleOpInterface` and accepts
tensors and memrefs
- also accepts target and source halo sizes; both are required for
proper lowering
* minor refactoring for testing partial MeshSharding equality
* Canonicalization for ShardingOp folding constant values into
respective `static_*` attributes
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