Function param_doc_entry_tokens 

pub(crate) fn param_doc_entry_tokens(
    cfg_attrs: &[Attribute],
    entry_ident: &Ident,
    placeholder: &str,
    several_ok: bool,
    choices_ty: &Type,
) -> TokenStream

Emit the MX_MATCH_ARG_PARAM_DOCS static + its linkme registration.