[KRDB] Write correct tooltip colors into gtkrc in kcminit

kcminit for performance reasons is not desktop settings aware which means it won't load the plasma integration plugin and as such
not apply the color scheme to Qt's widgets.
When writing the GTK config, it would read them from kdeglobals directly. However, for tooltips it would use QToolTip::palette()
which would then use Qt's default palette in kcminit. Use the QPalette we created from kdeglobals to get the tooltip colors instead.

CCBUG: 355540

Differential Revision: https://phabricator.kde.org/D18482