Shell: Add support for $0,$1,...

Author: https://github.com/alimpfard
Commit: 0b57cdff82
Pull-request: https://github.com/SerenityOS/serenity/pull/3473
Reviewed-by: https://github.com/bugaevc

Shell/main.cpp

@@ -209,6 +209,8 @@ int main(int argc, char** argv)
 
     parser.parse(argc, argv);
 
+    shell->current_script = argv[0];
+
     if (!skip_rc_files) {
         auto run_rc_file = [&](auto& name) {
             String file_path = name;