Fix for KT-9855: java.lang.IllegalAccessError when using private package level operator method

#KT-9855 Fixed

compiler/testData/codegen/box/private/kt9855.kt

@@ -0,0 +1,15 @@
+class MyString(var content : String)
+
+object Greeter {
+    fun sayHello(name : String): String {
+        var result = MyString(name)
+        result += "K"
+        return result.content
+    }
+}
+
+private operator fun MyString.plus(suffix: String) : MyString =  MyString("${this.content}$suffix")
+
+fun box(): String {
+    return Greeter.sayHello("O")
+}