Conform functions to extension functions and vice versa

#KT-5989 Fixed

idea/idea-completion/testData/basic/multifile/NotImportedExtensionFunction3/NotImportedExtensionFunction3.dependency.kt

@@ -6,14 +6,14 @@ fun (String.() -> Unit)?.helloFun1() {
 fun Function0<Unit>.helloFun2() {
 }
 
-fun ExtensionFunction0<String, Unit>.helloFun3() {
+fun @extension Function1<String, Unit>.helloFun3() {
 }
 
-fun ExtensionFunction0<Int, Unit>.helloFun4() {
+fun @extension Function1<Int, Unit>.helloFun4() {
 }
 
 fun Function1<String, Unit>.helloFun5() {
 }
 
 fun Any.helloAny() {
-}
+}

idea/idea-completion/testData/basic/multifile/NotImportedExtensionFunction3/NotImportedExtensionFunction3.kt

@@ -8,6 +8,6 @@ fun firstFun(p: String.() -> Unit) {
 // ABSENT: helloFun2
 // EXIST: helloFun3
 // ABSENT: helloFun4
-// ABSENT: helloFun5
+// EXIST: helloFun5
 // EXIST: helloAny
 // NOTHING_ELSE: true