Support 'is/as FunctionN<...>' and 'invoke' for KFunction instances

compiler/testData/codegen/box/reflection/functions/instanceOfFunction.kt

@@ -0,0 +1,36 @@
+// WITH_REFLECT
+// FILE: FromJava.java
+
+import kotlin.reflect.KCallable;
+import kotlin.jvm.functions.Function1;
+import kotlin.jvm.functions.Function2;
+import kotlin.jvm.functions.Function3;
+
+public class FromJava {
+    public static String test(KCallable<?> x) {
+        if (!(x instanceof Function1)) return "Fail 6";
+        if (!(x instanceof Function2)) return "Fail 7";
+        if (!(x instanceof Function3)) return "Fail 8";
+        return "OK";
+    }
+}
+
+// FILE: test.kt
+
+class Foo {
+    fun bar(x: Int): Int = x + 1
+}
+
+fun box(): String {
+    val bar = Foo::class.members.single { it.name == "bar" }
+
+    if (bar is Function1<*, *>) return "Fail 1"
+    if (bar !is Function2<*, *, *>) return "Fail 2"
+    if (bar is Function3<*, *, *, *>) return "Fail 3"
+
+    bar as? Function2<Foo, Int, Int> ?: return "Fail 4"
+
+    if (bar(Foo(), 42) != 43) return "Fail 5"
+
+    return FromJava.test(bar)
+}