testsuite batch97: prefix readonly-through-nameref declare error

[brianjfox]

Batch 97 — nameref test 237 → 235. Extends batch94's declare readonly-prefix conformance to the nameref case.

declare/typeset/local prefix a readonly-assignment failure with the builtin name, but only did so for a direct readonly variable. Assigning through a nameref to a readonly target fell through to Shell::set and printed the bare target name:

declare -r foo0=x; declare -n ref=foo0; declare ref=X
  bash:  declare: ref: readonly variable
  gnash: foo0: readonly variable      # bare, and leaks the target name

Now the nameref is resolved for the readonly test but the diagnostic reports the name as written (ref), matching bash. This also collapses the readonly empty-nameref case (typeset -n r; typeset -r r; typeset r=x) from gnash's bare-line-plus-prefixed-line to the single prefixed message bash prints.

ctest 22/22, run_diff all 234 scripts match bash. No regressions (varenv, declare unchanged).

The deeper nameref17 remainders (typeset +n/+r on a readonly nameref, function-scope readonly namerefs) and the quoted-vs-unquoted declare -n a=(...) compound-assignment distinction remain — the latter needs parse-time compound-assignment tracking gnash doesn't preserve in a builtin's argv.