Verify and consider using ConnectionDB for constrained insertion mode

[gonfunko]

#516 attempts to match the semantic ordering of connections when iterating through them to insert a block in constrained movement mode.

(1) This behavior should be verified for correctness
(2) We should decide if we want to use the Connection DB instead
(3) If yes, we should update the code to do so.

[gonfunko]

Closing since it's been two months and nobody has complained about the navigation order, which seems like good evidence that it's correct.