fix: register handler within init script

[susnux]

• Resolves: Files directly download from shared links instead of co-editing #4168
• Resolves: Files sometimes do not get opened immediately on internal links #3815
• Target version: main

Summary

Based on nextcloud/viewer#2922

This should fix all the loading order issues, we now have an API package.
So we can register the handler in an init script and thus its always registered.

I cannot test this locally due to missing dev setup of Collabora, maybe you could help me testing @elzody ?

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Documentation (manuals or wiki) has been updated or is not required

[susnux]

@luka-nextcloud do you plan to backport this? If yes then I will also backport the viewer

[luka-nextcloud]

/backport to stable30

[luka-nextcloud]

/backport to stable31

[luka-nextcloud]

@susnux Could you please review backport prs?

[mmeeks]

Wow this would be wonderful to have deployed - I'm still getting a ton of this ...

[pedropintosilva]

Thanks for not only fixing the problem but also backporting it! @susnux or @luka-nextcloud could you please press the button to create a new release of richdocuments? Otherwise, and until a new version is published, users will continue experiencing these problems.

[susnux]

Otherwise, and until a new version is published, users will continue experiencing these problems.

It does not work either until next maintenance releases of Nextcloud server.