Create from Usage: Make extension functions/properties 'private' by default

#KT-11799 Fixed

idea/testData/quickfix/createFromUsage/createFunction/unaryOperations/minusOnLibType.kt.after

@@ -5,6 +5,6 @@ fun test() {
     val a = -false
 }
 
-operator fun Boolean.unaryMinus(): Any {
+private operator fun Boolean.unaryMinus(): Any {
     TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
 }