Add $x_redirect_by in all places used wp_redirect() and wp_safe_redirect() - in the core, themes and plugins

[valentynilinov]

To better debug any redirects, please explicitly add the $x_redirect_by parameter in all places where the wp_redirect() and wp_safe_redirect() functions are used.

And also add a recommendation for theme and plugin developers to explicitly specify this parameter.

I think this will be useful for all developers in the future.