Summary:
This change implements forwarding the pointer gestures to the new API in
SeatInterface.

While screen is locked no gestures are forwarded to the server. Also
locking the screen cancels any active gesture. Similar if areas inside
KWin would start to intercept the gestures, they need to be cancelled on
the Wayland SeatInterface.

Test Plan: Not yet

Reviewers: #kwin, #plasma_on_wayland

Subscribers: plasma-devel, kwin

Tags: #plasma_on_wayland, #kwin

Differential Revision: https://phabricator.kde.org/D3174