Introduce a wrapper fro setcookie()

[Chouby]

Recent browsers expect the parameter samesite to be set. A new parameter sameparty is on its way too.

The old (PHP < 7.3) setcookie() signature doesn't accept these new parameters. It's however possible to set them with a hack.

I propose to introduce a new wp_set_cookie() function to support all versions of PHP. I also propose to introduce a filter in this function. This should help for #37000.

[Chouby]

The first patch is proposed for feedback on the function itself. It doesn't include the replacement of the current calls to setcookie() by wp_set_cookie().