egl/android: add aosp_nougat system/window.h back for back compat

Also layer ANativeWindow_* APIs on top of legacy APIs for api level less
than 26 in a new platform_android.h header.

v2: persist frozen system/window.h header

Signed-off-by: Yiwei Zhang <zzyiwei@chromium.org>
Reviewed-by: Rob Clark <robdclark@chromium.org> (v1)
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11286>

bin/update-android-headers.sh

@@ -15,6 +15,10 @@ fi
 
 dest=include/android_stub
 
+# Persist the frozen Android N system/window.h for backward compatibility
+
+cp -av ${dest}/system/window.h platform-system-core/libsystem/include/system
+
 rm -rf ${dest}
 mkdir ${dest}