Move screen inversion through XRandr into X11 standalone platform

Summary:
By moving the functionality into the Platform API we can also implement
support on other platforms which support this in general (e.g. DRM once
Roman's color adjustment patches landed).

Reviewers: KWin, Plasma

Subscribers: plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D7447