CommonHostInterface: Add a method to get top-level window handle

src/frontend-common/common_host_interface.h

@@ -192,6 +192,9 @@ public:
   /// Requests a resize to a multiple of the render window size.
   bool RequestRenderWindowScale(float scale);
 
+  /// Returns a pointer to the top-level window, needed by some controller interfaces.
+  virtual void* GetTopLevelWindowHandle() const;
+
   /// Opens a file in the DuckStation "package".
   /// This is the APK for Android builds, or the program directory for standalone builds.
   virtual std::unique_ptr<ByteStream> OpenPackageFile(const char* path, u32 flags) override;