Add global animation speed slider to workspace options KCM
Summary:
Introduce a new config entry into kdeglobals AnimationSpeed that will
control /all/ animation speeds in kwin and plasma themes and Qt styles
and kirigami.
The value stored is a multiplier.
i.e 1 == normal speed, 0.5 = twice as fast, 2 = twice as slow.
0 is a special value meaning "disable animations"
The QML is a bit complex to represent a logarithmic slider that goes
4x, 2x, 1x, 0.5x, 0.25x, 0.125x
but still allowing a user to type arbitrary values into their config
Test Plan: Looked at config
Reviewers: Plasma, broulik
Reviewed By: Plasma, broulik
Subscribers: ngraham, GB_2, broulik, anthonyfieroni, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D22885