[KCharSelect] Initially give focus to the search lineedit
Summary:
If the search lineedit widget is added, give it initial focus, so that you
launch the dialogue and start typing to find the character you want;
(much like a web browser).
Test Plan: make && ctest
Reviewers: Frameworks, cfeck
Subscribers: kde-frameworks-devel
Tags: Frameworks
Differential Revision: https://phabricator.kde.org/D29362