Use ECMGeneratePkgConfigFile to create the pkgconfig file.
Summary:
This also fixes the version in the .pc file.
BUG 390225
FIXED-IN: 5.55
Reviewers: cfeck, Build System, alexeymin
Reviewed By: alexeymin
Subscribers: alexeymin, kde-frameworks-devel
Tags: Frameworks
Differential Revision: https://phabricator.kde.org/D17718