QQC2-Desktop-Style: Convert license headers to SPDX expressions
Summary:
Convert license headers to SPDX expressions and add license texts
as required by REUSE specification.
Reviewers: ngraham, davidedmundson
Reviewed By: ngraham, davidedmundson
Subscribers: plasma-devel
Tags: Plasma
Maniphest Tasks: T11550
Differential Revision: https://phabricator.kde.org/D28382