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

plugins/allopen/testData/bytecodeListing/sealed.kt

@@ -0,0 +1,14 @@
+annotation class AllOpen
+
+@AllOpen
+sealed class Sealed {
+    class C1 : Sealed() {}
+    class C2 : Sealed() {}
+}
+
+sealed class Sealed2 {
+    @AllOpen
+    class C1 : Sealed2() {}
+
+    class C2 : Sealed2() {}
+}