Extension callables index and its use in completion

idea/testData/completion/basic/multifile/NotImportedExtensionFunction2/NotImportedExtensionFunction2.dependency.kt

@@ -0,0 +1,16 @@
+package second
+
+fun (() -> Unit)?.helloFun1() {
+}
+
+fun Function0<Unit>.helloFun2() {
+}
+
+fun ExtensionFunction0<String, Unit>.helloFun3() {
+}
+
+fun Function1<String, Unit>.helloFun4() {
+}
+
+fun Any.helloAny() {
+}

idea/testData/completion/basic/multifile/NotImportedExtensionFunction2/NotImportedExtensionFunction2.kt

@@ -0,0 +1,12 @@
+package first
+
+fun firstFun(p: () -> Unit) {
+    p.hello<caret>
+}
+
+// EXIST: helloFun1
+// EXIST: helloFun2
+// EXIST: helloAny
+// ABSENT: helloFun3
+// ABSENT: helloFun4
+// NUMBER: 3