[K/N] Avoid magic strings in KonanMangler

compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/mangle/MangleConstant.kt

@@ -47,5 +47,9 @@ enum class MangleConstant(val prefix: Char, val separator: Char, val suffix: Cha
         const val FUN_PREFIX = "kfun"
         const val CLASS_PREFIX = "kclass"
         const val FIELD_PREFIX = "kfield"
+
+        const val OBJC_MARK = "objc:"
+        const val OBJC_CONSTRUCTOR_MARK = "#Constructor"
+        const val OBJC_PROPERTY_ACCESSOR_MARK = "#Accessor"
     }
 }