Fix abstract method error: implement arity in function references

compiler/testData/codegen/boxWithStdlib/callableReference/function/getArityViaFunctionImpl.kt

@@ -0,0 +1,30 @@
+import kotlin.test.assertEquals
+import kotlin.jvm.internal.FunctionImpl
+
+fun test(f: Function<*>, arity: Int) {
+    assertEquals(arity, (f as FunctionImpl).getArity())
+}
+
+fun foo(s: String, i: Int) {}
+class A {
+    fun bar(s: String, i: Int) {}
+}
+fun Double.baz(s: String, i: Int) {}
+
+fun box(): String {
+    test(::foo, 2)
+    test(A::bar, 3)
+    test(Double::baz, 3)
+
+    test(::box, 0)
+
+    fun local(x: Int) {}
+    test(::local, 1)
+
+    test(fun(s: String) = s, 1)
+    test(fun(){}, 0)
+    test({}, 0)
+    test({x: Int -> x}, 1)
+
+    return "OK"
+}