Advertise wl_seat version 7
Created by: ascent12
This does not require any code changes, as we already copy the keymap data separately for each client.
For details, see wayland/wayland@905c0a34
Relevant code: https://github.com/swaywm/wlroots/blob/460a630a43c3aa914a84e2a2a0f879f8042d6c7f/types/seat/wlr_seat_keyboard.c#L346-L373
We could implement that with proper fd sealing, but since that's linux-specific, I doubt that's going to happen.