Merge "Updated Face AIDL createSession docs" into tm-dev

     * vold_prepare_subdirs.cpp). Implementations may store additional user-specific data, such as

     * embeddings or templates, in StrongBox.

     *

     * During create session it is expected that the HAL will call linkToDeath with the callee's

     * binder token. The recommended implementation is to close this session if the callee dies,

     * to prevent subsequent createSession calls from failing.

     *

     * @param sensorId The sensorId for which this session is being created.

     * @param userId The userId for which this session is being created.

     * @param cb A callback to notify the framework about the session's events.