[mlir][flang][openacc] Support device_type on loop construct (#76892)

This is adding support for `device_type` clause representation in the
OpenACC MLIR dialect on the acc.loop operation and adjust flang to lower
correctly to the new representation.

Each "value" that can be impacted by a `device_type` clause is now
associated with an array attribute that carry this information. This
includes:
- `worker` clause information
- `gang` clause information
- `vector` clause information
- `collapse` clause information
- `tile` clause information

The representation of the `gang` clause information has been updated and
all values are now carried in a single operand segment. This segment is
then subdivided by `device_type`. Each value in a segment is also
associated with a `GangArgType` so it can be differentiated
(num/dim/static). This simplify the handling of gang values an limit the
number of new attributes needed.

When the clause can be associated with the operation without any value
(`gang`, `vector`, `worker`). These are represented by a dedicated
attributes with device_type information.

Extra getter functions are provided to make it easier to retrieve a
value based on a device_type.