[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

generators/tests/org/jetbrains/kotlin/generators/tests/GenerateTests.kt

@@ -286,6 +286,9 @@ fun main(args: Array<String>) {
             testClass<AbstractFirPsiBytecodeListingTestForAllOpen> {
                 model("bytecodeListing", excludedPattern = excludedFirTestdataPattern)
             }
+            testClass<AbstractDiagnosticTestForAllOpenBase> {
+                model("diagnostics", excludedPattern = excludedFirTestdataPattern)
+            }
             testClass<AbstractFirLightTreeDiagnosticTestForAllOpen> {
                 model("diagnostics", excludedPattern = excludedFirTestdataPattern)
             }