Config Pages 3.0.0

First release using semantic versioning, replacing the 8.x-2.x series.

- Drupal 12 compatibility, hooks converted to OOP hook classes.
- Drupal 8 and 9 support dropped, core_version_requirement is ^10 || ^11 || ^12.
- Fixed the import confirmation redirect leading to the canonical route, which
  could result in editing a config page from a different language context.
- Fixed the module help page rendering empty.
- Limited allowed classes in the unserialize() call of the context data.
- Dependency injection cleanup across the entity handlers.

Contains a backwards compatibility break: the constructor signatures of
ConfigPagesForm, ConfigPagesListBuilder, ConfigPagesTypeListBuilder,
ConfigPagesController and ConfigPagesClearConfirmationForm changed.