[mlir][python] support taking ops instead of values in op constructors

Introduce support for accepting ops instead of values when constructing ops. A
single-result op can be used instead of a value, including in lists of values,
and any op can be used instead of a list of values. This is similar to, but
more powerful, than the C++ API that allows for implicitly casting an OpType to
Value if it is statically known to have a single result - the cast in Python is
based on the op dynamically having a single result, and also handles the
multi-result case. This allows to build IR in a more concise way:

    op = dialect.produce_multiple_results()
    other = dialect.produce_single_result()
    dialect.consume_multiple_results(other, op)

instead of having to access the results manually

    op = dialect.produce.multiple_results()
    other = dialect.produce_single_result()
    dialect.consume_multiple_results(other.result, op.operation.results)

The dispatch is implemented directly in Python and is triggered au...