MBS-13564: Correctly override primary on alias locale change

[reosarevok]

Fix MBS-13564

Problem

Attempting to change the locale of an alias marked as primary to one which already has a primary alias crashes with an ISE.

Solution

I noticed the issue is that we were not clearing the previous primary value first for this case, since we were only looking for a changed primary_for_locale. In this case the locale changes, not the primary_for_locale flag. This change ensures primary_for_locale is cleared upon either primary_for_locale or locale changes if primary_for_locale is being set or if it was already set and was not overriden by the row changes.

Testing

Manually, plus I added a test to Data::Alias. I'm also making Data::Alias less of a mess in a subsequent commit.

[yvanzo]

The commit does what it says it does, but there seems to be an issue with silently clearing the primary flag.

@mwiencek wrote in description of the related MBS-11896:

Avoiding duplicate primary locales can be handled by the application (and already is). If it wasn't, it even seems better to have the application fail with a unique index violation (since that indicates it's not accounting the changes properly) than silently change the data.

So it seems that the ISE is still the best to have until we make such data change visible in the editing process.

I didn’t check the tests for now but thank you still as it is always some amount of work.

[reosarevok]

I think this is what was meant by "can be handled by the application (and already is)." In every other case, we already do this with the primary flag, this just fixes one edge case where it crashed.