XWIKI-21633: Adding a step tour on a class field doesn't work

[Sereza7]

Jira URL

https://jira.xwiki.org/browse/XWIKI-21633

Changes

Description

• Removed XWiki interpretation from the JSON construction velocity template in TourJson
• Added a hint for the element field of the step creation/edition forms.
• Added a javascript log when the retrieval of the tour's JSON fails
• Added the english value for the element field hint.

Clarifications

• The main change is the one line in the TourJSon file.
  • We need one backslash to escape a special character in CSS. \
  • We escape this backslash when serializing the tour data to a JSON \\
• XWiki interpreter figures out it's the newline syntax and replaces it with \n
• The other changes in this PR are just small quality improvements:
  • Addition of a hint to the element field so that it's easier to use by admins
  • Addition of a failure message when retrieving the JSON for easier debugging (without it, this kind of tour failure was completely silent)

Screenshots & Video

Both of those screenshots are taken after applying the changes proposed in this PR:

Executed Tests

Successfully passed mvn clean install -f xwiki-platform-core/xwiki-platform-tour/ -Pquality,integration-tests,docker -Dxwiki.test.ui.wcag=true with no WCAG warning.

Expected merging strategy

• Prefers squash: Yes
• Backport on branches:
  • 16.10.X (localized changes, relatively safe)