[mlir][irdl] Support variadicity check in operations

This patch adds support for loading IRDL operations that are
using optional or variadics operands and results.

If an operation declares more than one optional/variadic operand
or result, then it requires the segment sizes in the attribute
dictionary, and otherwise it is computed using the number of
operands or results.

Currently, a variadic operand or result definiton expects all
operands and results in that definition to have the same type.
This restriction will be removed in a following patch.

Depends on D153983

Reviewed By: Mogball, unterumarmung

Differential Revision: https://reviews.llvm.org/D154073