What should we add?

Part of #9417. Depends on #9425. Will interact with other efforts in #8779.

The ConsolidateBlocks pass is run by default at optimisation level 3, and (albeit very uncommon in practice) is used by the synthesis routing method at all levels. This currently cannot support control-flow, primarily because the data format it reads has no way of representing that knowledge. Once a solution to #9425 is in place, this pass should be upgraded to use that information, and enter control-flow blocks where appropriate.

The implementation of the control-flow parts of this will likely end up looking quite similar to that of CommutativeCancellation: see #9423.