Add MultiFileHighlightingTest which checks that other files are not parsed during highlighting

idea/testData/multiFileHighlighting/delegatesReference.kt

@@ -0,0 +1,11 @@
+package test
+
+import delegates.*
+import util.*
+
+fun f() {
+    val d = D(C("", 0), object : T2 {})
+    d.anotherFun()
+    d.<error>invalidFun</error>()
+    WithDelegatedProperty().i
+}