java: add ThreadSafe query (P3)

Co-authored-by: Raúl Pardo <raul.pardo@protonmail.com>
Co-authored-by: SimonJorgensenMancofi <simon.jorgensen@mancofi.dk>
Co-authored-by: Bjørnar Haugstad Jåtten <bjornjaat@hotmail.com>

java/ql/test/query-tests/ThreadSafe/examples/Test3Super.java

@@ -0,0 +1,17 @@
+package examples;
+
+@ThreadSafe
+public class Test3Super extends Test2 {  // We might want an alert here for the inherited unsafe methods.
+
+  public Test3Super() {
+    super.x = 0;
+  }
+
+  public void y() {
+    super.x = 0;  //$ MISSING: Alert
+  }
+
+  public void yLst() {
+    super.lst.add("Hello!");  //$ MISSING: Alert
+  }
+}