[MLIR] Add a new Mesh dialect (#68007)

This is the 1st PR of [Mesh sharding
RFC](https://discourse.llvm.org/t/open-mlir-meeting-9-28-2023-rfc-sharding-framework-design-for-device-mesh/73695),
includes

Includes:

- mesh.cluster op
- mesh.shard op (the mesh.annotate op in the RFC slides, the name is
modified a bit from @stellaraccident 's advice, which I think might be a
bit more concise)
- MeshSharding attribute