Conditionally set SH_ScrollBar_LeftClickAbsolutePosition based on kdeglobals setting

Summary: CCBUG: 379498

Test Plan:

• Set ScrollbarLeftClickNavigatesByPage=true in the [KDE] section of ~/.config/kdeglobals
• Click in the scroll trough in a Qt/KDE app
• See that the scroll handle position jumps right there
• Set ScrollbarLeftClickNavigatesByPage=false or remove it from kdeglobals
• Click in the scroll trough in a Qt/KDE app
• See that the scroll handle moves up or down by one page height

Reviewers: Frameworks, Plasma

Subscribers: broulik, kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D25360