lua.window.setPosition: add param waitForSync

if waitForSync is false, then SDL_SyncWindow is not called, and so the
method may return before the requested changes actually happen.

This is backwards-compatible with previous behaviour

src/modules/window/Window.h

@@ -189,7 +189,7 @@ public:
 
 	virtual void getDesktopDimensions(int displayindex, int &width, int &height) const = 0;
 
-	virtual void setPosition(int x, int y, int displayindex) = 0;
+	virtual void setPosition(int x, int y, int displayindex, bool waitForSync) = 0;
 	virtual void getPosition(int &x, int &y, int &displayindex) = 0;
 
 	virtual Rect getSafeArea() const = 0;

src/modules/window/sdl/Window.cpp

@@ -957,7 +957,7 @@ void Window::getDesktopDimensions(int displayindex, int &width, int &height) con
 	}
 }
 
-void Window::setPosition(int x, int y, int displayindex)
+void Window::setPosition(int x, int y, int displayindex, bool waitForSync)
 {
 	if (!window)
 		return;
@@ -974,7 +974,8 @@ void Window::setPosition(int x, int y, int displayindex)
 	y += displaybounds.y;
 
 	SDL_SetWindowPosition(window, x, y);
-	SDL_SyncWindow(window);
+	if (waitForSync)
+		SDL_SyncWindow(window);
 
 	settings.useposition = true;
 }

src/modules/window/sdl/Window.h

@@ -66,7 +66,7 @@ public:
 
 	void getDesktopDimensions(int displayindex, int &width, int &height) const override;
 
-	void setPosition(int x, int y, int displayindex) override;
+	void setPosition(int x, int y, int displayindex, bool waitForSync) override;
 	void getPosition(int &x, int &y, int &displayindex) override;
 
 	Rect getSafeArea() const override;

src/modules/window/wrap_Window.cpp

@@ -384,8 +384,9 @@ int w_setPosition(lua_State *L)
 		int x_unused, y_unused;
 		instance()->getPosition(x_unused, y_unused, displayindex);
 	}
+	bool waitForSync = luax_optboolean(L, 4, true);
 
-	instance()->setPosition(x, y, displayindex);
+	instance()->setPosition(x, y, displayindex, waitForSync);
 	return 0;
 }