[Flang][OpenMP][Lower] Use clause operand structures

This patch updates Flang lowering to use the new set of OpenMP clause operand
structures and their groupings into directive-specific sets of clause operands.

It simplifies the passing of information from the clause processor and the
creation of operations.

The `DataSharingProcessor` is slightly modified to not hold delayed
privatization state. Instead, optional arguments are added to `processStep1`
which are only passed when delayed privatization is used. This enables using
the clause operand structure for `private` and removes the need for the ad-hoc
`DelayedPrivatizationInfo` structure.

The processing of the `schedule` clause is updated to process the `chunk`
modifier rather than requiring two separate calls to the `ClauseProcessor`.

Lowering of a block-associated `ordered` construct is updated to emit a TODO
error if the `simd` clause is specified, since it is not currently supported by
the `ClauseProcessor` or later compilation stages.

Removed processing of `schedule` from `omp.simdloop`, as it doesn't apply to
`simd` constructs.