KT-4977 Smart completion should work for arguments in brackets

#KT-4977 Fixed

idea/idea-completion/testData/handlers/smart/GetWithBrackets.kt

@@ -0,0 +1,5 @@
+fun foo(map: Map<String, Int>, p: String) {
+    map[<caret>]
+}
+
+// ELEMENT: p

idea/idea-completion/testData/handlers/smart/GetWithBrackets.kt.after

@@ -0,0 +1,5 @@
+fun foo(map: Map<String, Int>, p: String) {
+    map[p]<caret>
+}
+
+// ELEMENT: p

idea/idea-completion/testData/handlers/smart/SetWithBrackets.kt

@@ -0,0 +1,5 @@
+fun foo(map: Map<String, Int>, p: String) {
+    map[<caret>] = 1
+}
+
+// ELEMENT: p

idea/idea-completion/testData/handlers/smart/SetWithBrackets.kt.after

@@ -0,0 +1,5 @@
+fun foo(map: Map<String, Int>, p: String) {
+    map[p]<caret> = 1
+}
+
+// ELEMENT: p

idea/idea-completion/testData/smart/heuristicSignatures/GetWithBrackets.kt

@@ -0,0 +1,6 @@
+fun foo(map: Map<String, Int>, p1: Any, p2: String) {
+    map[<caret>]
+}
+
+// ABSENT: p1
+// EXIST: p2