Add support for pointer gestures to nested Wayland platform

Summary:
To ease development of touchpad gestures it's useful to have support in
the nested Wayland platform.

Test Plan: Shown in Debug Console of nested KWin

Reviewers: KWin, Plasma

Subscribers: plasma-devel, kwin

Tags: KWin

Differential Revision: https://phabricator.kde.org/D5059