LLVM IR Dialect: port DimOp lowering from the translator

DimOp is converted to a constant LLVM IR dialect operation for static
dimensions and to an access to the dynamic size info stored in the memref
descriptor for the dynamic dimensions.  This behavior is consistent with the
existing mlir-translator.

This completes the porting of MLIR -> LLVM lowering to the dialect conversion
infrastructure.

PiperOrigin-RevId: 233665634