Reconcile SQL MV function behavior on SQL arrays

The docs say that SQL MV_* functions all work on arrays:

> All 'array' references in the multi-value string function documentation can refer to multi-value string columns or ARRAY literals.

But it isn't true. Many of them (MV_SLICE, MV_CONCAT, others) have signatures that do not accept SQL ARRAY types. We should either make these functions work on SQL ARRAYs, or update the docs to say that they do not.

Start by comparing the multi-value string function documentation with the SQL signatures for MV_SLICE, MV_CONCAT, and the other affected MV_* functions. Determine whether the documented ARRAY behavior or the function support should change; done means the documentation and SQL ARRAY behavior consistently describe the same supported set.

Written by the indexing model from the issue text.