Java: Move dataflow based model generation testcases to a subfolder.

java/ql/test/utils/model-generator/dataflow/p/ImmutablePojo.java

@@ -0,0 +1,26 @@
+package p;
+
+public final class ImmutablePojo {
+
+    private final String value;
+
+    private final long x;
+
+    public ImmutablePojo(String value, int x) {
+        this.value = value;
+        this.x = x;
+    }
+
+    public String getValue() {
+        return value;
+    }
+
+    public long getX() {
+        return x;
+    }
+
+    public String or(String defaultValue) {
+        return value != null ? value : defaultValue;
+    }
+
+}