Switch JetMultifileBasicCompletionTest to generated approach

idea/testData/completion/basic/multifile/ExtensionOnNullable.dependency.kt

@@ -0,0 +1,14 @@
+package second
+
+fun String.helloFun() {
+}
+
+fun String.helloWithParams(i : Int) : String {
+    return ""
+}
+
+fun String.helloFunPreventAutoInsert() {
+}
+
+fun Int.helloFake() {
+}