tooltipmanager: use qstyle wakeup delay instead of hardcoding

Summary:
aids in making kinfocenter and systemsettings behave with the
same delay. plus not hardcoding things is always cool

BUG: 393722
FIXED-IN: 5.18.0

Test Plan: builds, tooltip shows up, qdebugging says timeout is now 700

Reviewers: mart

Reviewed By: mart

Subscribers: mart, ngraham, bcooksley, plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D26733