[AllOpen] Private properties can be considered stable even when open

The AllOpen plugin can make private members open. But for private
properties, they can be considered stable for smart-casting if they do
not have a custom getter.

#KT-58049 Fixed

plugins/allopen/testData/diagnostics/kt54260.kt

@@ -1,10 +1,9 @@
-// FIR_IDENTICAL
 // WITH_STDLIB
 
 annotation class AllOpen
 
 @AllOpen
 annotation class ConsoleCommands(
-    val <!NON_FINAL_MEMBER_IN_FINAL_CLASS!>value<!>: String = "",
-    val <!NON_FINAL_MEMBER_IN_FINAL_CLASS!>scope<!>: String
+    val value: String = "",
+    val scope: String
 )