Allow SQLServer Sequence/HiLo on non-key properties

[roji]

And add some migration test coverage.

Closes #29758

[AndriySvyryd]

Also add a test that uses the sequence and calls SaveChanges

[ghost]

Hello @roji!

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[ghost]

Apologies, while this PR appears ready to be merged, I've been configured to only merge when all checks have explicitly passed. The following integrations have not reported any progress on their checks and are blocking auto-merge:

1. Azure Pipelines

These integrations are possibly never going to report a check, and unblocking auto-merge likely requires a human being to update my configuration to exempt these integrations from requiring a passing check.

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