Add icon loader

Add helper to load icons from image files via FFmpeg.

app/src/icon.h

@@ -0,0 +1,16 @@
+#ifndef ICON_H
+#define ICON_H
+
+#include "common.h"
+
+#include <stdbool.h>
+#include <SDL2/SDL.h>
+#include <libavformat/avformat.h>
+
+SDL_Surface *
+scrcpy_icon_load(void);
+
+void
+scrcpy_icon_destroy(SDL_Surface *icon);
+
+#endif