Java: add java.util.stream models

Author: Jami Cogswell

java/ql/lib/ext/java.util.stream.model.yml

@@ -92,4 +92,7 @@ extensions:
       pack: codeql/java-all
       extensible: neutralModel
     data:
+      - ["java.util.stream", "Collectors", "joining", "(CharSequence)", "manual"]
       - ["java.util.stream", "Collectors", "toList", "()", "manual"]
+      - ["java.util.stream", "Collectors", "toMap", "(Function,Function)", "manual"]
+      - ["java.util.stream", "Collectors", "toSet", "()", "manual"]