Create factory methods in all API classes

[Art4]

Declaring the classes in the Redmine\Api\ namespace as final will allow us to make more future changes without worrying to much about BC.

To achieve this in a FC way we could create new factory methods create(HttpClient $client): self in all API child classes.

class ProjectApi extends AbstractApi
{
    final public static function create(HttpClient $client): self
    {
        return new self($client);
    }

    /**
     * @param Client|HttpClient $client
     */
    final public function __construct($client)
    {
        if (get_called_class() !== __CLASS__) {
            @trigger_error('Extending ' . __CLASS__ . ' is deprecated since v2.x, it will become final in v3.0.0.');
        }

        if ($client instanceof Client) {
            $this->client = $client;
        }

        // Handle HttpClient...
    }
}

Using the HttpClient in the API classes makes the AbstractApi obsolete and can be deprecated. Extending it should also trigger a deprecation.

abstract class AbstractApi 
{
    /**
     * @param Client|HttpClient $client
     */
    public function __construct($client)
    {
        @trigger_error(__CLASS__ . ' is deprecated since v2.x and will be removed in v3.0.0.');

        // old code...
    }
}

Affected classes

1. Redmine\Api\Attachment
2. Redmine\Api\CustomField
3. Redmine\Api\Group
4. Redmine\Api\Issue
5. Redmine\Api\IssueCategory
6. Redmine\Api\IssuePriority
7. Redmine\Api\IssueRelation
8. Redmine\Api\IssueStatus
9. Redmine\Api\Membership
10. Redmine\Api\News
11. Redmine\Api\Project
12. Redmine\Api\Query
13. Redmine\Api\Role
14. Redmine\Api\Search
15. Redmine\Api\TimeEntry
16. Redmine\Api\TimeEntryActivity
17. Redmine\Api\Tracker
18. Redmine\Api\User
19. Redmine\Api\Version
20. Redmine\Api\Wiki
21. Redmine\Api\AbstractApi