Completion tests: added ability to test presentation text attributes

idea/testData/completion/smart/BooleanExpected.kt

@@ -1,5 +1,5 @@
 fun foo(): Boolean = <caret>
 
-// EXIST: true
-// EXIST: false
+// EXIST: { itemText: "true", attributes: "bold" }
+// EXIST: { itemText: "false", attributes: "bold" }
 // ABSENT: Boolean

idea/testData/completion/smart/Null.kt

@@ -4,4 +4,4 @@ fun bar() {
     foo(<caret>)
 }
 
-// EXIST: null
+// EXIST: { itemText: "null", attributes: "bold" }