fix: failed token generation on public shares

[elzody]

• Target version: main

Summary

This is part of an effort to improve public sharing on the main branch with all the server changes for NC 31.
The issue here was that the sharing token was grabbed from an invisible html element that contained the token, which is no longer present -- the token instead must be gotten via either initial state from files_sharing or via this method using the @nextcloud/sharing library which I think is clearer. It also will be helpful for other things relating to public shares

https://nextcloud-libraries.github.io/nextcloud-sharing/modules/public.html

Checklist

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

[juliusknorr]

There seem to be other occurrences where shareToken is still obtained from an element by id, maybe worth to check those as well separately if they are still in use