[KDeclarative] Port from deprecated QWheelEvent::delta() to angleDelta()

Summary:
I'm assuming we don't want to rename the property just yet, for SC?
Are the TODO KF6 correct?

Test Plan: Builds

Reviewers: mart, davidedmundson

Reviewed By: davidedmundson

Subscribers: aacid, kde-frameworks-devel

Tags: Frameworks

Maniphest Tasks: T11553

Differential Revision: https://phabricator.kde.org/D23894