Lots of work on focus management

Source/Integration/LuprexViewportClient.h

@@ -0,0 +1,28 @@
+////////////////////////////////////////////////////////////
+//
+// LuprexViewportClient.h
+//
+// Custom game viewport client.  Implements a project-wide
+// click-to-focus rule: when a left-mouse-button click is
+// not handled by any widget and bubbles up to the viewport,
+// we hit-test under the cursor and focus the nearest
+// focusable ancestor of whatever was hit.
+//
+////////////////////////////////////////////////////////////
+
+#pragma once
+
+#include "CoreMinimal.h"
+#include "Engine/GameViewportClient.h"
+#include "LuprexViewportClient.generated.h"
+
+UCLASS()
+class INTEGRATION_API UlxViewportClient : public UGameViewportClient
+{
+	GENERATED_BODY()
+
+public:
+	UlxViewportClient(const FObjectInitializer &ObjectInitializer);
+
+	virtual bool InputKey(const FInputKeyEventArgs &EventArgs) override;
+};