[GTK] change the way of registering DeviceOrientation clients.

[GTK] change the way of registering DeviceOrientation clients.
https://bugs.webkit.org/show_bug.cgi?id=78680

Reviewed by Gustavo Noronha Silva.

Bug 78085 removed deviceOrientationClient and deviceMotionClient from PageClients. Instead,
DeviceOrientationClient and DeviceMotionClient should be registered by PageSupplement class.
Chromium, mac and qt ports are already changed by Bug 78085.

* webkit/webkitwebview.cpp:
(webkit_web_view_init):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@108151 268f45cc-cd09-0410-ab3c-d52691b4dbfc