Fixed KT-4318 Keyword should be selected in completion if there's exact match

#KT-4318 Fixed

idea/testData/completion/weighers/ExactMatchForKeyword.kt

@@ -0,0 +1,11 @@
+fun test() {
+    val ifMore = true
+    val isFirst = true
+    if<caret>
+}
+
+// ORDER: if
+// ORDER: ifMore
+// ORDER: isFirst
+// ORDER: ifn
+// SELECTED: 0