[php] return type declarations

If I have this extern for a CakePHP class

package cake.orm;

import php.NativeArray;

@:native("Cake\\ORM\\Table")
extern class Table {
        function initialize(config:NativeArray):Void;
}

And this subclass

package app.model.table;

import cake.orm.Table;

class CookiesTable extends Table
{
        override function initialize(config):Void
        {
        }

}

Then this php is emitted

namespace app\model\table;
.....
       /**
         * @param array $config
         *
         * @return void
         */
        public function initialize ($config) {

But initialize() has a return type declaration from CakePHP 4 onward so this doesn't work too well:

class Table {
    public function initialize(array $config): void

It would be nice if extern methods could be annotated as having a return type so the compiler would emit overrides with the correct type.

Start from the extern method declaration and the emitted PHP override shown in the issue, then trace how the PHP backend emits method signatures. Done means an extern annotation can carry a return type and generated PHP overrides match the CakePHP declaration, with coverage for this example.