resolvectl: use compat status string instead of a field-by-field table

The status string is modeled after our --version output: +enabled -disabled equals=more-info

For example:
     Protocols: -DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=allow-downgrade/supported

src/basic/string-util.h

@@ -53,6 +53,10 @@ static inline const char* true_false(bool b) {
         return b ? "true" : "false";
 }
 
+static inline const char* plus_minus(bool b) {
+        return b ? "+" : "-";
+}
+
 static inline const char* one_zero(bool b) {
         return b ? "1" : "0";
 }