reuse same parser for '(co)datatype(_new)' as for 'bnf_decl'
reuse same parser for '(co)datatype(_new)' as for 'bnf_decl'

MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle