j2k: flatten test cases and testData directory structure

Move j2k/test/tests -> j2k/tests, j2k/test/testData -> j2k/testData

j2k/testData/multiFile/GetterAndSetterUsages/2.java

@@ -0,0 +1,12 @@
+class B {
+    void foo(AAA a) {
+        a.setX(a.getX() + 1);
+        y += "a";
+    }
+
+    private String y = "";
+
+    public String getYY() {
+        return y;
+    }
+}