Use Kirigami.ActionTextField for the SearchField
Summary: Need Kirigami latest version (master)
Test Plan: A regression found (need D19300)
Reviewers: Discover Software Store, ngraham
Reviewed By: Discover Software Store, ngraham
Subscribers: ngraham, apol, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D19301