"add operator modifier" fix handles fake overrides

#KT-9347 Fixed

idea/testData/quickfix/modifiers/operatorModifierInherited.kt

@@ -0,0 +1,10 @@
+// "Add 'operator' modifier" "true"
+open class Foo {
+    fun get(idx: Int): Any = 5
+}
+
+object Bar : Foo()
+
+fun test(): Any {
+    return Bar<caret>[5]
+}

idea/testData/quickfix/modifiers/operatorModifierInherited.kt.after

@@ -0,0 +1,10 @@
+// "Add 'operator' modifier" "true"
+open class Foo {
+    operator fun get(idx: Int): Any = 5
+}
+
+object Bar : Foo()
+
+fun test(): Any {
+    return Bar<caret>[5]
+}