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/TurnstileExample.java

@@ -0,0 +1,23 @@
+package examples;
+
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
+
+@ThreadSafe
+public class TurnstileExample {
+  private Lock lock = new ReentrantLock();
+  private int count = 0;
+
+  public void inc() {
+    Lock l = lock;
+    l.lock();
+    count++;
+    l.unlock();
+  }
+
+  public void dec() {
+    lock.lock();
+    count--;
+    lock.unlock();
+  }
+}