Fix tag foreign key violation in storage removal

Carsten Hartenfelsrequested to merge
hartenfels/krita:feature/storagepurge into master

By first gathering the tag ids to delete into a temporary table and then deleting them from all tables that reference the tags table before deleting from the tags table itself. Previously, it would try to delete the tags before the tag storages that references them and didn't delete tag translations or resource tag assignments at all.

Cf. https://krita-artists.org/t/krita-5-3-6-0-beta-thread/165015/102

Test Plan

  • Import a bundle with tags into Krita.
  • Exit Krita.
  • Delete the .bundle file in ~/.local/share/krita or other OS-equivalent.
  • Start Krita. Observe that it starts up now instead of crashing with an error about not being able to remove the storage.

Formalities Checklist

  • I confirmed this builds.
  • I confirmed Krita ran and the relevant functions work.
  • I tested the relevant unit tests and can confirm they are not broken. (If not possible, don't hesitate to ask for help!)
  • I made sure my commits build individually and have good descriptions as per KDE guidelines.
  • I made sure my code conforms to the standards set in the HACKING file.
  • I can confirm the code is licensed and attributed appropriately, and that unattributed code is mine, as per KDE Licensing Policy.
  • Does the patch add a user-visible feature? If yes, is there a documentation MR ready for it at Krita Documentation Repository?

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