[mlir] Add a MemRefCastOp canonicalization pattern.

Summary:
This revision adds a conservative canonicalization pattern for MemRefCastOp that are typically inserted during ViewOp and SubViewOp canonicalization.
Ideally such canonicalizations would propagate the type to consumers but this is not a local behavior. As a consequence MemRefCastOp are introduced to keep type compatibility but need to be cleaned up later, in the case where more dynamic behavior than necessary is introduced.

Differential Revision: https://reviews.llvm.org/D79438