teach 'create from usage' to add 'operator' modifier when necessary

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

@@ -1,7 +1,7 @@
 // "Create member function 'inc'" "true"
 
 class A<T>(val n: T) {
-    fun inc(): A<T> {
+    operator fun inc(): A<T> {
         throw UnsupportedOperationException("not implemented") //To change body of created functions use File | Settings | File Templates.
     }
 }

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

@@ -3,7 +3,7 @@
 class A<T>(val n: T) {
     fun minus(n: Int): A<T> = throw Exception()
 
-    fun minus(): A<T> {
+    operator fun minus(): A<T> {
         throw UnsupportedOperationException("not implemented") //To change body of created functions use File | Settings | File Templates.
     }
 }

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

@@ -4,6 +4,6 @@ fun test() {
     val a = -false
 }
 
-fun Boolean.minus(): Any {
+operator fun Boolean.minus(): Any {
     throw UnsupportedOperationException("not implemented") //To change body of created functions use File | Settings | File Templates.
 }

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

@@ -1,7 +1,7 @@
 // "Create member function 'minus'" "true"
 
 class A<T>(val n: T) {
-    fun minus(): Any {
+    operator fun minus(): Any {
         throw UnsupportedOperationException("not implemented") //To change body of created functions use File | Settings | File Templates.
     }
 }

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

@@ -1,7 +1,7 @@
 // "Create member function 'minus'" "true"
 
 class A<T>(val n: T) {
-    fun minus(): A<T> {
+    operator fun minus(): A<T> {
         throw UnsupportedOperationException("not implemented") //To change body of created functions use File | Settings | File Templates.
     }
 }