Userland: Convert command line arguments to String/StringView

StringView was used where possible. Some utilities still use libc
functions which expect null-terminated strings, so String objects were
used there instead.

Userland/Utilities/chgrp.cpp

@@ -16,7 +16,7 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
     TRY(Core::System::pledge("stdio rpath chown"));
 
     char const* gid_arg = nullptr;
-    char const* path = nullptr;
+    StringView path {};
     bool dont_follow_symlinks = false;
 
     Core::ArgsParser args_parser;