Allow cast to be used in constant expressions

[mvorisek]

Description

repro: https://3v4l.org/OVu3r

<?php

declare(strict_types=1);

class Foo
{
    public const MAX_LARGE_LENGTH_BYTES = 1024 + 1; // 1 KiB + 1 %
    public const MAX_LARGE_LENGTH_BYTES2 = (int) (1024 * 1.01);
}

var_dump(Foo::MAX_LARGE_LENGTH_BYTES);
var_dump(Foo::MAX_LARGE_LENGTH_BYTES2);

Currently + is supported, but cast is not. But all of these are operators with constant result /wo side effects where the arguments are constant.

[nielsdos]

I think this makes sense. I'll think a bit about it and maybe provide a patch.