refs #22529 [finc, vufind] w3c + amsl sources

* w3c
** help: use same userLang for xml as for lang in meta tag
** add help.phtml to update html5 DocType
** adv help: use hyphens for name props
** search help: use hyphens for name props
** adv help: restore changes in root from #18999 - moved to finc accessibility
** sources list: remove href from button
** sources list: remove stray end tag for dfg link
** sources list: remove invalid and unused itemcount

* fix urls of sources list
** use url encoded quotion mark for base url
** do not use external link view helper

co-authored by: Alexander Purr <purr@ub.uni-leipzig.de>
* w3c cart / bookbag: remove redundant value="1"