[mlir][ods] OpFormat: fix type inference issues

This patch fixes issues with generating assembly format parsers for
operations that use the `operands` directive or which have unnamed
arguments or results.

This patch also fixes a function in `OpAsmParser` that always produced
an error when trying to resolve variadic operands with the same type.

Fixes #51841

Reviewed By: rriddle

Differential Revision: https://reviews.llvm.org/D131627