rules: Added extended wild cards <none>, <some> and <any> Added the following wild cards to the rules file syntax, in addition to the current `*` legacy wild card: - `<none>`: Match *empty* value. - `<some>`: Match *non-empty* value. - `<any>`: Match *any* (optionally empty) value. Its behavior does not depend on the context, contrary to the legacy wild card `*`. This will enable writing much simpler rules, see [!764] for an example of tricky rules in the `xkeyboard-config` project, that would benefit from the new wild cards. [!764]: https://gitlab.freedesktop.org/xkeyboard-config/xkeyboard-config/-/merge_requests/764 The verbose wild cards are preferred to single characters: - More intuitive: self-explanatory. - Does not steal syntax from other token. - Extensible syntax, should we need it. A previous proposal used the characters (`!`, `+`, `?`) for their similarity with the corresponding syntax of regular expressions (negative assertion & quantifiers), in line with `*`. But `!` is not that intuitive after all and conflict with its role as section header. Furthermore, `+` is also used as a merge mode. Finally, nothing beats whole short words for readability.