fix(help): Gloss over globals with flatten

When using globals, people tend to make all of the top-level arguments
global and cascading them through would just bloat the output.

clap_builder/src/output/help_template.rs

@@ -525,7 +525,7 @@ impl<'cmd, 'writer> HelpTemplate<'cmd, 'writer> {
                 };
                 let args = subcommand
                     .get_arguments()
-                    .filter(|arg| should_show_arg(self.use_long, arg))
+                    .filter(|arg| should_show_arg(self.use_long, arg) && !arg.is_global_set())
                     .collect::<Vec<_>>();
                 sub_help.write_args(&args, heading, option_sort_key);
             }

tests/builder/help.rs

@@ -3109,9 +3109,8 @@ Options:
   -h, --help             Print help
 
 parent test:
-      --child <child>    
-      --parent <parent>  
-  -h, --help             Print help
+      --child <child>  
+  -h, --help           Print help
 
 parent help:
   [COMMAND]...  Print help for the subcommand(s)