HPCC-11356/HPCC-11354 WU Helpers page should selectively allow download/showContent

Do not show content for "dll"
Do not allow download of "ECL"

Fixes HPCC-11356
Fixes HPCC-11354

Signed-off-by: Gordon Smith <gordon.smith@lexisnexis.com>
Merge pull request #5825 from GordonSmith/HPCC-11356

HPCC-11356/HPCC-11354 WU Helpers page should selectively allow download/...

Reviewed-By: Miguel Vazquez <miguel.vazquez@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>