Introduce yield_groups()

[lippserd]

This PR introduces yield_groups() to yield sets of items from a sorted iterator grouped by a specific criterion gathered from a callback:

namespace ipl\Html\Example;

use Generator;
use Iterator;

use function ipl\Stdlib\yield_groups;

class YieldGroupsExample
{
    /**
     * @param Iterator<int, object{category: int, id: string, data: string}> $data
     *
     * @return Generator<int, array<int, object{category: int, id: string, data: string}>>
     */
    public function groupByCategory(Iterator $data): Generator
    {
        return yield_groups($data, function ($v): int {
            return $v->category;
        });
    }

    /**
     * @param Iterator<int, object{category: int, id: string, data: string}> $data
     *
     * @return Generator<int, array<int, string>>
     */
    public function groupByCategoryWithDataAsValue(Iterator $data): Generator
    {
        return yield_groups($data, function ($v): array {
            return [$v->category, $v->data];
        });
    }

    /**
     * @param Iterator<int, object{category: int, id: string, data: string}> $data
     *
     * @return Generator<int, array<string, string>>
     */
    public function groupByCategoryWithDataAsValueAndIdAsKey(Iterator $data): Generator
    {
        return yield_groups($data, function ($v): array {
            return [$v->category, $v->data, $v->id];
        });
    }
}

[yhabteab]

Tested with: https://github.com/Icinga/icingaweb2-module-x509/pull/185/files#diff-e248f67b3802079b7e7cfc304f1873fba6c74e354a37c22e6bc56443a15f813dR505-R512

[nilmerg]

I've just fixed the phpstan complaints: https://github.com/Icinga/ipl-stdlib/actions/runs/5975237958