Improve the way in which we connect the non reachable `JumpTargets` when
rebuilding the dispatcher for non `SemanticsPreserving` `CFGForm`s.
When connecting group of jump targets that are not currently reachable
from the entry dispatcher, we elect the jump target with the lowest
program counter value, as the one to be connected to the dispatcher.
We also mark the jump targets now transitively reachables from the
elected one, as reachable, so to avoid adding other unnecessary edges
from the dispatcher.
Andrea Gussoni
8125a19379