Remove the window parameter from the render() function of all the renderers

This makes for a slimmer API and instead we can create the renderer <-> window association
behind the scenes ourselves,
in set_component.

api/cpp/tests/manual/platform_native/windowadapter_win.h

@@ -82,7 +82,7 @@ struct MyWindowAdapter : public slint_platform::WindowAdapter
 
     void render()
     {
-        m_renderer->render(window());
+        m_renderer->render();
         if (has_active_animations())
             request_redraw();
     }

api/cpp/tests/manual/platform_qt/main.cpp

@@ -83,7 +83,7 @@ public:
     {
         slint_platform::update_timers_and_animations();
 
-        m_renderer->render(window());
+        m_renderer->render();
 
         if (has_active_animations()) {
             requestUpdate();