KT-12068 Special completion item for "[]" get-operator access

#KT-12068 Fixed

idea/idea-completion/testData/basic/common/getOperator/Extension.kt

@@ -0,0 +1,11 @@
+package p
+
+class C
+
+operator fun C.get(p: Int): Int = 0
+
+fun foo(c: C) {
+    c.<caret>
+}
+
+// EXIST: { lookupString: "[]", itemText: "[]", tailText: "(p: Int) for C in p", typeText: "Int", attributes: "bold" }

idea/idea-completion/testData/basic/common/getOperator/NotForSafeCall.kt

@@ -0,0 +1,5 @@
+fun some(list: List<String>?) {
+    list?.<caret>
+}
+
+// ABSENT: "[]"

idea/idea-completion/testData/basic/common/getOperator/Simple.kt

@@ -0,0 +1,5 @@
+fun some(list: List<String>) {
+    list.<caret>
+}
+
+// EXIST: { lookupString: "[]", itemText: "[]", tailText: "(index: Int)", typeText: "String", attributes: "bold" }