Load last saved GUI configuration on first load.

Also save theme to the configuration.

PiperOrigin-RevId: 843710929
Change-Id: I7ce9ce0f026d2cb5f79addf6c16c9b540bf11954

src/experimental/studio/app.h

@@ -90,6 +90,7 @@ class App {
   // UI state that is transient and only needed while the application runs
   struct UiTempState {
     bool should_exit = false;
+    bool first_frame = true;
 
     // Windows.
     bool help = false;