Fixup navigations to/from join entity when new many-to-many relationship is created

[ajcvickers]

Fixes #26779

Also cleanup of delay-fixup/suspended detection logic, and tests for #26074.

[ajcvickers]

/azp run

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Azure Pipelines successfully started running 1 pipeline(s).

[ajcvickers]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[AndriySvyryd]

Why are you changing this? Is there a way that something could be added to _danglingJoinEntities during CompleteDelayedFixup()?

[ajcvickers]

I don't believe so. However, BeginDelayedFixup can be called again, and we clear any existing danglers when this happens. This shouldn't be needed if everything is working correctly, but it is there against the possibility that some error happens when, for example, attaching the graph, and we leave the collection in a bad state. We could not do this, but it felt slightly more robust to keep doing it.

[AndriySvyryd]

I agree that this is more robust, but I'd prefer us to throw when an error happens rather than try to keep consistency.

You could throw in BeginDelayedFixup if _inAttachGraph is false and _danglingJoinEntities is not empty

[ajcvickers]

Done.

[AndriySvyryd]

You don't need to call ToList() anymore.

Also could avoid some allocations if you don't null-out _danglingJoinEntities

[ajcvickers]

Do you think it's better to keep the list around (even though it may not be used again, or not used for some time) rather than create a new one if we happen to need it again? (I've been wondering about this.)

[AndriySvyryd]

I think that the chance of the list being used goes up significantly after it has been used once.