KWayland: Convert license headers to SPDX
Summary:
Convert license headers to SPDX expressions and add license files as
required by REUSE specification.
Reviewers: zzag
Reviewed By: zzag
Subscribers: kde-frameworks-devel
Tags: Frameworks
Maniphest Tasks: T11550
Differential Revision: https://phabricator.kde.org/D28058