Remove generated codegen tests, move all testData to box/

A single test file will be generated out of box/ directory

compiler/testData/codegen/box/defaultArguments/function/extentionFunctionInClassObject.kt

@@ -0,0 +1,17 @@
+class A {
+  class object {
+    fun Int.foo(a: Int = 1): Int {
+        return a
+    }
+
+    fun test(): String {
+        if (1.foo() != 1) return "fail"
+        if (1.foo(2) != 2) return "fail"
+        return "OK"
+    }
+  }
+}
+
+fun box(): String  {
+   return A.test()
+}