JVM_IR: fix default argument stub visibility.

Match the rules from the old backend:

1. Private and inline only methods get package private default
   argument stubs.

2. Everything else is public.

compiler/testData/writeFlags/function/withDefaultArguments/funInClass.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND: JVM_IR
 open class MyClass() {
     fun testPublic(s: String = "") {}