Move built-in integrations, such as with Doctrine ORM, to a separate bundles

[Kreyu]

To make the core bundle as small as possible, each integration with optional third party libraries, such as Doctrine ORM or PHPSpreadsheet, should be moved to separate repositories. This will allow for updating and improving each integration without bumping a version of the core (for example, to prevent updating the bundle for projects not using those 3rd party libraries).