Allopen: Handle allopen annotations on classes (KT-12149)

plugins/allopen/testData/bytecodeListing/nestedInner.kt

@@ -0,0 +1,14 @@
+annotation class AllOpen
+
+@AllOpen
+class Test {
+    fun testMethod() {}
+
+    class Nested {
+        fun nestedMethod() {}
+    }
+
+    inner class Inner {
+        fun innerMethod() {}
+    }
+}