Events: Post NotifyButtonPress only for ET_MOUSE_RELEASED event types.

Currently, we post NotifyButtonPress for every ButtonNotify callback.
NotifyButtonPress is used to activate a new window. Window should be
activated only when the button is released and not when pressed. This
CL makes changes to ensure NotifyButtonPress event is posted only
after button is released and not when pressed.
DRWH: Introduce RootWindowHostDelegateWayland class.

DRWH has many roles like maintaining native window state
changes, window manager for open windows, window activation etc.
This CL introduces RootWindowHostDelegateWayland which implements
necessary support for dispatching native events and
window management. This will be taken into use by DRWH in a follow
up CL.
DRWH: Take RootWindowHostDelegateWayland into use.

This CL makes changes in DRWH to take RootWindowHostDelegateWayland
into use.