Deprecate suggestName

Summary: KCoreAddons now has a drop-in replacement. Deprecate this so it can be removed in KF6

Test Plan: Buils. Deprecation warnings are thrown due to internal use that will be ported in a future patch

Reviewers: dfaure

Reviewed By: dfaure

Subscribers: kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D22637