Allowed call value with extension function type as simple function type.

compiler/testData/diagnostics/tests/resolve/invoke/extensionValueAsNonExtension.kt

@@ -0,0 +1,22 @@
+// !DIAGNOSTICS: -UNUSED_EXPRESSION -UNUSED_PARAMETER -UNUSED_VARIABLE
+class A
+
+fun test(foo: A.() -> Int, a: A) {
+    val b: Int = foo(a)
+    val c: Int = (foo)(a)
+}
+
+class B {
+    val foo: A.() -> Int = null!!
+
+    init {
+        val b: Int = foo(A())
+    }
+}
+
+fun foo(): A.() -> Int {
+    val b: Int = foo()(A())
+    val c: Int = (foo())(A())
+
+    <!UNREACHABLE_CODE!>return<!> null!!
+}