Fix for KT-5150: Accessors for private methods are not generated for get/set conventions

#KT-5150 Fixed

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

@@ -0,0 +1,21 @@
+var result = "fail"
+
+private operator fun X.get(name: String) = name + "K"
+private operator fun X.set(name: String, v: String) {
+    result = v
+}
+
+class X {
+    fun test() : String {
+        if (this["O"] != "OK") return "fail 1: ${this["O"]}"
+
+        this["O"] += "K"
+        if (result != "OKK") return "fail 2: ${result}"
+
+        return "OK"
+    }
+}
+
+fun box(): String {
+    return X().test()
+}