XWIKI-17010: Code viewer doesn't allow to copy blank lines

[Sereza5]

Jira URL

https://jira.xwiki.org/browse/XWIKI-17010

Changes

Description

• Replaced the "empty" lines with a single newline character.

Clarifications

• The empty lines did not have any text content so they are not kept in the clipboard at all. However, the clipboard adds a newline in between two separate nodes in the copied text. By making sure there's at least a newline character in the "empty line" node, we make sure the clipboard registers it. I don't have sources backing my logic, but in my manual tests it worked well.

Executed Tests

Manual tests on my local instance (both with and without author blame).
Built the change with mvn clean install -f xwiki-platform-core/xwiki-platform-flamingo/xwiki-platform-flamingo-skin/xwiki-platform-flamingo-skin-resources -Pquality. Since this is a very niche use case and was quite badly broken, I suppose none of our tests ever relied on copying code from this viewer (in addition, a WCAG scan on the page shows that there's a WCAG contrast error on this UI, it'd have been found by CI if we had any automated test passing on this viewer).

Expected merging strategy

• Prefers squash: Yes
• Backport on branches:
  • 17.10.X (small scope bugfix)

[github-actions]

💚 All backports created successfully

Status	Branch	Result
✅	stable-17.10.x
✅	stable-18.4.x

Questions ?

Please refer to the Backport tool documentation and see the Github Action logs for details