Prevent usage of callable objects in ReflectionFunction::__construct()

As per @weirdan's feedback, we can prevent
the usage of `object` instances that
implement `__invoke()`, as well as `array`
callables, by declaring the ctor argument of
`ReflectionFunction` to be either a real `Closure`,
or a `callable-string`.

While this may not be 100% of scenarios, it is a
healthy way to identify errors in userland.

Ref: https://github.com/vimeo/psalm/pull/8722#discussion_r1027151421

stubs/Reflection.phpstub

@@ -432,7 +432,11 @@ abstract class ReflectionFunctionAbstract implements Reflector
 
 class ReflectionFunction extends ReflectionFunctionAbstract
 {
-    /** @psalm-pure */
+    /**
+     * @param callable-string|Closure $function
+     *
+     * @psalm-pure
+     */
     public function __construct(callable $function) {}
 
     /**