Stop DisplayPollThread in StopProcessingEvents.

StartProcessingEvents starts the thread with options and starts polling.
StopProcessingEvents stops polling for wayland events but doesn't
actually stop the thread. This patch fixes it.
This is based on initial work done here:
https://github.com/baillaw/ozone-wayland/commit/142abd2525a39ef2ad5c356e9a53987d35039a98
Combine Create and SetWidgetAttributes to one IPC.

Currently, we send an IPC to create the window, then an IPC call to
set the window type (i.e. Popup, FrameLess etc). This patch combines
them both into one Create IPC call.
IPC: No need to pass size information as part of SetWidgetState.

State Change handling in Display doesn't use the size information
being passed as part of WaylandWindow_State. WaylandWindow_State
doesn't accept size attributes anymore.