Qt Core API review

Review the API in Qt Core:

Grouped by subdirectory:

• animations: Only small changes, OK
• global: OK
• io: OK, mainly addition of std::filesystem::path based APIs
• itemmodels: OK
• kernel: OK with the exceptions below
  • QProperty and friends
  • QMetaType/QVariant/Q*Iterable
• mimetypes: No changes
• plugin: OK
• serialization: OK, only larger changes in the xml stream reader
• text
• thread
  • Partially: QThread and friends are ok, once https://codereview.qt-project.org/c/qt/qtbase/+/312743 merges
  • QFuture, QPromise and friends (+Qt Concurrent) need a more in depth review
• time: Some smaller issues
• tools