Create from Usage: Add operator modifier to indexing get/set functions

#KT-10185 Fixed

idea/testData/quickfix/createFromUsage/createFunction/set/createSetFromUsage2.kt.after

@@ -8,6 +8,6 @@ class Foo<T> {
     }
 }
 
-fun <T> Any.set(s: String, w: ArrayList<T>, value: ArrayList<T>) {
+operator fun <T> Any.set(s: String, w: ArrayList<T>, value: ArrayList<T>) {
     throw UnsupportedOperationException("not implemented") //To change body of created functions use File | Settings | File Templates.
 }