LibCore+Everywhere: Remove ArgsParser::add*(char const*&)

This is not guaranteed to always work correctly as ArgsParser deals in
StringViews and might have a non-properly-null-terminated string as a
value. As a bonus, using StringView (and DeprecatedString where
necessary) leads to nicer looking code too :^)

Userland/Services/TelnetServer/main.cpp

@@ -86,7 +86,7 @@ static void run_command(int ptm_fd, DeprecatedString command)
 ErrorOr<int> serenity_main(Main::Arguments arguments)
 {
     int port = 23;
-    char const* command = "";
+    StringView command = ""sv;
 
     Core::ArgsParser args_parser;
     args_parser.add_option(port, "Port to listen on", nullptr, 'p', "port");