j2k: flatten test cases and testData directory structure

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

j2k/testData/fileOrElement/thisExpression/classAdotThisFoo.kt

@@ -0,0 +1,14 @@
+package a.b
+
+open class Base {
+    fun foo() {
+    }
+}
+
+class A : Base() {
+    inner class C {
+        fun test() {
+            this@A.foo()
+        }
+    }
+}