[Kickoff] Make the search field always look like a search field

Summary:
This patch makes Kickoff's search field always look like a search field, instead of only after you start typing. Functionality remains the same (with the exception of the hidden info display, which moves to underneath the user name)

BUG: 397581
BUG: 398276
BUG: 398278
FIXED-IN: 5.15.0

Test Plan:

All functionality still works:

Reviewers: Plasma, VDG, davidedmundson, abetts

Reviewed By: Plasma, VDG, abetts

Subscribers: cfeck, acrouthamel, fabianr, huftis, rooty, sharvey, romangg, broulik, safaalfulaij, oysteins, filipf, abetts, davidedmundson, michaeltunnell, plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D15011