Extract Win32 runtime state storage

src/platform_windows/windows_runtime_state.cpp

@@ -0,0 +1,34 @@
+#include "pch.h"
+
+#include "platform_windows/windows_runtime_state.h"
+
+#include "app.h"
+#include "wacom.h"
+
+namespace pp::platform::windows {
+namespace {
+
+struct RetainedWindowsRuntimeState final {
+    std::unique_ptr<App> owned_app;
+    WacomTablet tablet;
+};
+
+[[nodiscard]] RetainedWindowsRuntimeState& retained_runtime_state() noexcept
+{
+    static RetainedWindowsRuntimeState state;
+    return state;
+}
+
+}
+
+std::unique_ptr<App>& retained_owned_app() noexcept
+{
+    return retained_runtime_state().owned_app;
+}
+
+WacomTablet& retained_wacom_tablet() noexcept
+{
+    return retained_runtime_state().tablet;
+}
+
+}