[nostalgia/core] Add focusWindow, cleanup GLFW leak into Userland, change shutdown to stop main loop

src/nostalgia/core/gba/gfx.cpp

@@ -103,6 +103,9 @@ ox::Error shutdownGfx(Context*) noexcept {
 void setWindowTitle(Context*, const char*) noexcept {
 }
 
+void focusWindow(Context*) noexcept {
+}
+
 int getScreenWidth(Context*) noexcept {
 	return 240;
 }