[KLIB][tests] Reorganize "klib dump-metadata" tests

- Keep the test data under "native/native.tests/testData/klib/" dir
- Rename tests from "klib contents" to "klib dump-metadata"

native/native.tests/testData/klib/dump-metadata/builtinsSerializer/nestedClassesAndObjects.kt

@@ -0,0 +1,35 @@
+package test
+
+class ClassA {
+    class classB {
+        fun memberFromB(): Int = 100
+
+        class BC {
+            val memberFromBB: Int = 150
+        }
+
+        object BO {
+            val memberFromBO: Int = 175
+        }
+    }
+
+    inner class classC {
+        val memberFromC: Int = 200
+    }
+}
+
+class E {
+    companion object {
+        val stat: Int = 250
+
+        class D {
+            val memberFromD: Int = 275
+        }
+    }
+}
+
+class F {
+    object ObjA {
+        val memberFromObjA: Int = 300
+    }
+}