[mlir] FunctionOpInterface: arg and result attrs dispatch to interface

This patch removes the `arg_attrs` and `res_attrs` named attributes as a
requirement for FunctionOpInterface and replaces them with interface
methods for the getters, setters, and removers of the relevent
attributes. This allows operations to use their own storage for the
argument and result attributes.

Depends on D139471

Reviewed By: rriddle

Differential Revision: https://reviews.llvm.org/D139472