chrome: Standardize fullscreen transition behavor/callbacks (fixes #3571)

Use the same code path for all fullscreen transitions so that Chrome UI updates
correctly. All user-initiated fullscreen transitions now result in
CefWindowDelegate::OnWindowFullscreenTransition callbacks.

tests/cefclient/browser/window_test_runner.cc

@@ -36,6 +36,10 @@ void WindowTestRunner::ModifyBounds(const CefRect& display, CefRect& window) {
   }
 }
 
+void WindowTestRunner::Fullscreen(CefRefPtr<CefBrowser> browser) {
+  NOTIMPLEMENTED();
+}
+
 void WindowTestRunner::SetTitleBarHeight(CefRefPtr<CefBrowser> browser,
                                          const std::optional<float>& height) {
   NOTIMPLEMENTED();