wayland: use touch serials for drag_window, drag_resize_window and show_window_menu

[hojjatabdollahi]

Window::drag_window() on Wayland passes the pointer's last button serial to xdg_toplevel.move. Touch input never records a serial, so the request carries a stale pointer serial. Compositors validate the serial against the active implicit grab and reject the request, so client-side decorations cannot be dragged. (The same for resize, and window_menu).

Here's what I'm doing:

• Record (WlSeat, serial) on the WindowState in the touch down handler.
• Clear it in up once no other finger remains on that surface, and in cancel.
• In drag_window, drag_resize_window and show_window_menu, prefer the stored touch serial when a finger is down on the window and fall back to the pointer serial otherwise.

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• Tested on all platforms changed
  • it only touches Wayland
• Added an entry to the changelog module if knowledge of this change could be valuable to users
• Updated documentation to reflect any user-facing changes, including notes of platform-specific behavior
• Created or updated an example program if it would help users understand this functionality