STRPOS and POSITION

[gord02]

The subtrait function strpos was mapped to calcite's POSITION function in this PR.

I believe the two are not one to one mappings of one another as the semantics agruments are swapped. Substrait describes strpos, as the second arugment being the substring, while calcite's position, has the first argument being the substring.

[benbellick]

@bestbeforetoday sorry to @ you here, but it looks like a function you may have added in. Perhaps you may have some more context. 🙏

@gord02 I agree upon first glance that that seems backwards. I am not so familiar with the isthmus part of the codebase here. Anyone have any idea how hard it is to represent a mapping with the parameters swapped?