[5.0.1] Use topological sort to detect identifying relationship cycles. #23320
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Fixes #23289
Description
EF Core 5.0 adds validation that detects identifying relationship cycles to prevent infinite recursion. However the algorithm used returned false positive for multiple paths.
Customer Impact
Users who have identifying relationships with multiple paths in their model are unable to use them.
How found
User-reported for 5.0.0
Test coverage
Added in this PR.
Regression?
Yes, the affected scenario worked correctly in 3.1
Risk
Low. The topological sort implementation has been in use since 1.0 and is thoroughly tested.