Improve ability to expand array accesses to full range accesses when we have an elemental function

[LonelyCat124]

Currently we create a Codeblock for WHERE accesses like Rob found in UKCA:

WHERE(ABS(pivot) < min_pivot) pivot = min_pivot)

Since we have information on the Intrinsic (and non-intrisic call, which currently behaves wrong) on the is_elemental status, we can do better.

The basic idea of this fix is to modify fparser2.py line 4396 onwards to do:

            is_elemental = intrinsic_ancestor is not None and intrinsic_ancestor.is_elemental
            if (isinstance(ref.symbol, DataSymbol) and
                 (not intrinsic_ancestor or (intrinsic_ancestor and is_elemental))):

We should also be careful, and if is_elemental is None we should still create a codeblock, as in that case we don't know the status of the is_elemental result so its not safe for us to turn the WHERE statement into a Loop.