[TASK] Avoid inline JavaScript in backend update signals

BackendUtility::getUpdateSignalCode() returned plain inline JavaScript
code which got replaced by new BackendUtility::getUpdateSignalDetails().

The new function is capable of handling inline JavaScript code (for
backward compatibility reasons) and HTML markup using corresponding
`<typo3-immediate-action>` custom element.

OpendocsToolbarItem::updateNumberOfOpenDocsHook has been adjusted as
well to use the script-less implementation.

Resolves: #96002
Resolves: #96012
Releases: master, 11.5
Change-Id: I248db207600ae5c7452471a093f84f3802050c59
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/72206


Tested-by: core-ci <typo3@b13.com>
Tested-by: Jochen <rothjochen@gmail.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Jochen <rothjochen@gmail.com>
Reviewed-by: Oliver Bartsch <bo@cedev.de>