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/LegacyViewportCameraController.cpp

@@ -404,7 +404,7 @@ bool LegacyViewportCameraControllerInstance::HandleInputChannelEvent(const AzFra
     }
     else if (auto key = GetKeyboardKey(event.m_inputChannel); key != Qt::Key_unknown)
     {
-        if (state == InputChannel::State::Ended)
+        if (!event.m_inputChannel.IsActive())
         {
             m_pressedKeys.erase(key);
         }

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()

Code/Framework/AzFramework/AzFramework/Viewport/CameraInput.cpp

@@ -747,19 +747,23 @@ namespace AzFramework
                 return button == inputChannelId;
             });
 
-        if (inputChannelId == InputDeviceMouse::Movement::X)
+        // Accept active mouse channel updates, inactive movement channels will just have a 0 delta.
+        if (inputChannel.IsActive())
         {
-            return HorizontalMotionEvent{ aznumeric_cast<int>(inputChannel.GetValue()) };
-        }
-        else if (inputChannelId == InputDeviceMouse::Movement::Y)
-        {
-            return VerticalMotionEvent{ aznumeric_cast<int>(inputChannel.GetValue()) };
-        }
-        else if (inputChannelId == InputDeviceMouse::Movement::Z)
-        {
-            return ScrollEvent{ inputChannel.GetValue() };
+            if (inputChannelId == InputDeviceMouse::Movement::X)
+            {
+                return HorizontalMotionEvent{ aznumeric_cast<int>(inputChannel.GetValue()) };
+            }
+            else if (inputChannelId == InputDeviceMouse::Movement::Y)
+            {
+                return VerticalMotionEvent{ aznumeric_cast<int>(inputChannel.GetValue()) };
+            }
+            else if (inputChannelId == InputDeviceMouse::Movement::Z)
+            {
+                return ScrollEvent{ inputChannel.GetValue() };
+            }
         }
-        else if (wasMouseButton || InputDeviceKeyboard::IsKeyboardDevice(inputDeviceId))
+        if (wasMouseButton || InputDeviceKeyboard::IsKeyboardDevice(inputDeviceId))
         {
             return DiscreteInputEvent{ inputChannelId, inputChannel.GetState() };
         }