Add Editable.toString flow step

java/ql/test/library-tests/frameworks/android/widget/TestWidget.java

@@ -0,0 +1,11 @@
+import android.widget.EditText;
+
+public class TestWidget {
+
+    private void sink(Object sink) {}
+
+    public void test(EditText t) {
+        sink(t.getText().toString()); // $ hasTaintFlow
+    }
+}
+