Move ExtendedCursor::Shape's doc comment to the correct place
Summary:
It probably has to be placed above the enum, though I'm not sure whether
it applies to ExtendedCursor::Shape or CursorShape.
Test Plan: Compiles.
Reviewers: KWin, apol
Reviewed By: apol
Subscribers: kwin
Tags: KWin
Differential Revision: https://phabricator.kde.org/D18669