* MSQ: Validate that strings and string arrays are not mixed.
When multi-value strings and string arrays coexist in the same column,
it causes problems with "classic MVD" style queries such as:
select * from wikipedia -- fails at runtime
select count(*) from wikipedia where flags = 'B' -- fails at planning time
select flags, count(*) from wikipedia group by 1 -- fails at runtime
To avoid these problems, this patch adds type verification for INSERT
and REPLACE. It is targeted: the only type changes that are blocked are
string-to-array and array-to-string. There is also a way to exclude
certain columns from the type checks, if the user really knows what
they're doing.
* Fixes.
* Tests and docs and error messages.
* More docs.
* Adjustments.
* Adjust message.
* Fix tests.
* Fix test in DV mode.
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