Fix StackOverflow with self-loop bridges

[blegat]

This is breaking for a user relying on the fact that SingleBridgeOptimizer was creating the constraint to the same model recursively.
It would have been used in a non-stackoverflow situation in case a bridge would create a constraint of the same time as the constraint being transformed twice and then not. I would guess no user was doing that but we never know.

Closes #1015

[odow]

Potentially split the documentation updates and StackOverflow into two PRs?

[blegat]

Yes, I moved it to #1465, I will also create a separate PR for the Variable.SetMap as it will be useful for creating the variable identity bridges used for testing