MBS-14220: Add _conflicting_entity_path when missing

[reosarevok]

Fix MBS-14220

Problem

Trying to remove the disambiguation in a specific release group series causes an ISE. While this is the only RG series of this name, there's a release series of the same name (a duplicate, and in fact probably the RG series should be dropped). This was then hitting a broken error check.

Solution

Edit::Generic::Edit says:
Sub-classes that consume Edit::Role::CheckDuplicates are required to implement _conflicting_entity_path. N.B. This is not checked at compile-time.

This was not the case for a fair amount of them, including all the ::Create edits and both Place:: and Series::Edit.

This is a hard issue to hit. AFAICT it only causes issues when entering an edit removing a disambiguation that would cause the entity to clash with another entity of the same type and with no disambiguation. This happens relatively often with artists but it is unsurprising it took a long time for someone to hit it and report it for series.

With the current implementation, I'm not sure we actually need this on ::Create edits, but it probably cannot hurt to future-proof them just in case.

Testing

Manually, adding series of the same name with and without a disambiguation and then trying to blank the disambiguation of the one that had it. It originally ISEd, with this change it correctly leaves the "we couldn't apply this" edit note instead.