xcursor: search cursors in XDG_DATA_DIRS

[emersion]

We currently have a hardcoded list of paths:

#define XCURSORPATH "~/.icons:/usr/share/icons:/usr/share/pixmaps:~/.cursors:/usr/share/cursors/xorg-x11:"ICONDIR

From the spec:

If $XDG_DATA_HOME is either not set or empty, a default equal to $HOME/.local/share should be used.

If $XDG_DATA_DIRS is either not set or empty, a value equal to /usr/local/share/:/usr/share/ should be used.

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wlroots has migrated to gitlab.freedesktop.org. This issue has been moved to:

https://gitlab.freedesktop.org/wlroots/wlroots/-/issues/980

[emersion]

wayland-cursor patch for this: https://gitlab.freedesktop.org/wayland/wayland/-/merge_requests/112