[client] imgui: convert help overlay to use imgui

client/include/app.h

@@ -138,9 +138,4 @@ void app_releaseKeybind(KeybindHandle * handle);
  */
 void app_releaseAllKeybinds(void);
 
-/**
- * Changes whether the help message is displayed or not.
- */
-void app_showHelp(bool show);
-
 #endif

client/include/overlay_utils.h

@@ -27,7 +27,10 @@
 extern "C" {
 #endif
 
+typedef struct ImVec2 ImVec2;
+
 void overlayGetImGuiRect(struct Rect * rect);
+ImVec2 * overlayGetScreenSize(void);
 void imGuiResetStyle(void);
 
 #ifdef __cplusplus