More camera fixes for the new CameraInput system (#667)

* use new ViewportContext interface to set camera transform on load

* WIP fixes for camera viewport handler callbacks

* disable synchonization with old camera when new camera system is enabled

* further updates to camera-input

* ensure event is signalled when camera transform is set

* updates to ModernViewportCameraController

* fix for right click menu appearing with camera

* updates following review feedback

* convert std:: usage to AZStd::

Gems/Atom/RPI/Code/Source/RPI.Public/ViewportContext.cpp

@@ -205,6 +205,7 @@ namespace AZ
         {
             const auto view = GetDefaultView();
             view->SetCameraTransform(AZ::Matrix3x4::CreateFromTransform(transform.GetOrthogonalized()));
+            m_viewMatrixChangedEvent.Signal(view->GetWorldToViewMatrix());
         }
 
         void ViewportContext::SetDefaultView(ViewPtr view)