Various pieces of QTZP and QTZ rely (by using std::set_union or std::set_intersection) on the backends supplying the list of available IDs in sorted order. As this isn't documented as part of public API behavior, document it internally and assert it. Add the missing sorting and uniquification for Android; although the Java API used does appear to return a sorted list, its specification [0] says nothing about its ordering, so make sure. In the process, rename a wantonly long variable so the uniquifying doesn't need a line-split. [0] https://docs.oracle.com/javase/8/docs/api/java/util/TimeZone.html#getAvailableIDs-- Document, in the ICU backend, that the relevant API doesn't say what order it returns; but also make clear where the backend *does* take care of sorting it and rendering entries unique. Change-Id: I61b4ecf342044e2303b18889c600da5922aec278 Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>