Add Qt API to access underlying surface on Android

Currently, a patch to deliver QtWindow through WinId is on the way:
https://codereview.qt-project.org/c/qt/qtbase/+/511975

However, the QtWindow, which subclasses Android View, is not the actual surface that rendering happens. To find the actual surface, One has to find the underlying QtSurface (Android SurfaceView) from QtWindow first, then call Android SDK to get surface from QtSurface. Let alone one has to find QtWindow first right now (as of Dec. 2023 when the patch above has not been merged yet).

Such limitation imposes great difficulties for someone who want to use OpenGL to render onto surface directly. Passing WinId to OpenGL is easily doable on Window but needs excessive amount of JNI coding on Android. And such JNI coding requires Android SDK even Qt for Android internal Java APIs.