[DeedleFake]

Why

Kawa wants to support xdg-activation-v1 so that a window gets focus only when it presents a token tied to recent user input. Today a window started from a terminal never gets focus, and only windows opened through kawa's New are focused when they map. The kawa side is DeedleFake/kawa#18, stacked on DeedleFake/kawa#17. This PR adds only the wlroots bindings it needs.

Scope

All of these are plain 1:1 wrappers with no behavior of their own.

• CreateXDGActivationV1 wraps wlr_xdg_activation_v1_create.
• XDGActivationV1.OnRequestActivate and OnNewToken attach to the request_activate and new_token signals.
• XDGActivationV1.CreateToken wraps wlr_xdg_activation_token_v1_create, so the compositor can hand a token to programs it starts.
• XDGActivationV1RequestActivateEvent exposes the event's token and surface.
• XDGActivationTokenV1 exposes Valid, the surface, seat and serial fields, Name (from wlr_xdg_activation_token_v1_get_name) and OnDestroy.
• Seat.Valid lets a caller tell whether a token came with a seat, which is how wlroots marks a token made from a real input serial.

Tradeoffs

I left out bindings kawa doesn't use yet, such as wlr_xdg_activation_v1_find_token, the token timeout fields and the app ID. Each is a one-line addition when something needs it.

Blast Radius

These are new types and methods only. No existing binding changes, so other users of the package are unaffected.

Verification

go build ./... and go vet ./... pass against wlroots 0.20. Kawa's xdg-activation branch builds against this branch, and I exercised it on a real Xvfb session. A token from a click is granted focus, both before and after the window maps. A token without a serial is refused and marked for attention. A token kawa creates for New is accepted.