[NI] Fix extension function check after commonization

`isExtensionFunction` property is false for suspend functions

compiler/testData/codegen/box/inference/suspendExtensionRecevierFromConstraint.kt

@@ -0,0 +1,20 @@
+// WITH_RUNTIME
+// KJS_WITH_FULL_RUNTIME
+// !LANGUAGE: +NewInference
+
+class ExtensionReceiver
+typealias SuspendExtensionFunction = suspend ExtensionReceiver.() -> Unit
+suspend fun ExtensionReceiver.extensionMethod() {}
+
+fun test() {
+    val map = mutableMapOf<Unit, SuspendExtensionFunction>()
+
+    map[Unit] = {
+        extensionMethod()
+    }
+}
+
+fun box(): String {
+    test()
+    return "OK"
+}