Harden a few pieces of viewport controller logic

-Don't eat mouse/keyboard release events in the ViewportManipulatorController
-Do a key activity check in the LegacyViewportCameraController instead of checking state (this could be done elsewhere but it seems to be working as-is and is scheduled to go away)
-Ignore idle mouse delta updates sent to the modular camera controller

Signed-off-by: nvsickle <nvsickle@amazon.com>

Code/Editor/ViewportManipulatorController.cpp

@@ -216,7 +216,8 @@ namespace SandboxEditor
                 interactionHandled, AzToolsFramework::GetEntityContextId(), targetInteractionEvent, mouseInteractionEvent);
         }
 
-        return interactionHandled;
+        // Only filter button/key press events, not release events
+        return interactionHandled && event.m_inputChannel.IsActive();
     }
 
     void ViewportManipulatorControllerInstance::ResetInputChannels()