[AI] The ZoneGraph show flag is in the ZoneGraphEditor module but used during runtime in ZoneGraph module

The show flag for ZoneGraph lives in the ZoneGraphEditor module, but it is used for debugging at runtime by the main ZoneGraph module. There are protections around the type of build and some for EDITOR_ONLY, but these do not completely encapsulate the flag's usage. The ability to see ZoneGraph navigation data in a debug/development build is highly useful and in line with how the navmesh system operates.

1. Package the CitySample project for Debug or Development Standalone on PC
2. Open the packaged game
3. Once the level has loaded, enter the console command "Show Navigation"

Expected Result: ZoneGraph shapes are shown for the road and sidewalk where traffic and the crowd can move around.

Actual Result: Game crashes for missing show flag.

UnrealEditor_Engine!FEngineShowFlags::GetSingleFlag()
UnrealEditor_ZoneGraph!`UZoneShapeComponent::CreateSceneProxy'::`2'::FZoneShapeSceneProxy::GetViewRelevance()
UnrealEditor_Renderer!FRelevancePacket::ComputeRelevance()
UnrealEditor_Renderer!`FRelevancePacket::LaunchComputeRelevanceTask'::`12'::<lambda_1>::operator()()
UnrealEditor_Renderer!UE::Tasks::private::FTaskBase::TryExecuteTask()
UnrealEditor_Renderer!LowLevelTasks::TTaskDelegate<LowLevelTasks::FTask * __ptr64 __cdecl(bool),48>::TTaskDelegateImpl<`LowLevelTasks::FTask::Init<`UE::Tasks::private::FTaskBase::Init'::`2'::<lambda_1> >'::`13'::<lambda_1>,0>::CallAndMove()
UnrealEditor_Core!LowLevelTasks::FTask::ExecuteTask()
UnrealEditor_Core!LowLevelTasks::FScheduler::ExecuteTask()
UnrealEditor_Core!LowLevelTasks::FScheduler::WorkerLoop()
UnrealEditor_Core!`LowLevelTasks::FScheduler::CreateWorker'::`2'::<lambda_1>::operator()()
UnrealEditor_Core!FThreadImpl::Run()
UnrealEditor_Core!FRunnableThreadWin::Run()