fix(OCP): Fix Image interface

[provokateurin]

• Resolves: Fix/move image to oc namespace #47535 (comment)

Summary

Using a private class in the public interface leads to no methods being resolved. Thus it needs to implement \OCP\IImage.
\OCP\IImage is also missing some methods that were relied on in OC_Image by other apps (e.g. Talk nextcloud/spreed#13197) and needed to be added.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)