refactor(apps): Declare strict types where missing

[provokateurin]

Summary

Done with rector. The CI is going to fail, as not everything is working correctly yet.

Feel free to contribute a few fixes to resolve these problems. (if they are part of the app logic please make a separate PR and backport it, if it is just tests then you can push them on this branch)

@miaulalala already did a bunch of fixes to the dav app at the conf. Quite often it is actually the tests that provide wrong data while the application logic is just fine.

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)

[nickvergessen]

• I am against a mass-change like this 🙈
  As I had to experience myself it can have hidden issues that are not straight forward to debug with "random" side-effects fix(versions): Fix strict trimming of version paths files_accesscontrol#595
• There will be cases that are not covered by tests or integration tests and it will be a huge pain to discover and draw it back to this. Especially in the file related handling.

[provokateurin]

Makes sense, would you be fine if I limit it to apps with very high test coverage?
It's still useful to test it once, even if we don't enable it in the end, as it will point us to problems we can fix either way.

[provokateurin]

#58194