Java: Add support for flow through side-effects on static fields.

java/ql/test/library-tests/dataflow/fields/G.java

@@ -0,0 +1,21 @@
+public class G {
+  static Object[] f;
+
+  void sink(Object o) { }
+
+  void runsink() {
+    sink(f[0]);
+  }
+
+  void test1() {
+    f[0] = new Object();
+  }
+
+  void test2() {
+    addObj(f);
+  }
+
+  void addObj(Object[] xs) {
+    xs[0] = new Object();
+  }
+}