[XLA] Reuse utilities for type conversion between XLA and MLIR across XLA-related dialects
[XLA] Reuse utilities for type conversion between XLA and MLIR across XLA-related dialects

This CL moves the type conversion utilities from the MHLO dialect to `tensorflow/compiler/xla/mlir/utils/type_util.cc`, where they can be reused across other XLA-related MLIR dialects.
