XWIKI-9874: Introduce getLastError() in the Wiki Script Service.
XWIKI-9883: Unable to save a new wiki descriptor with the script service

* Add unit tests too.
* Rename some private methods in test classes in wiki-template-script and wiki-user-script.
Merge branch 'master' of github.com:xwiki/xwiki-platform
XWIKI-9874: Introduce getLastError() in the Wiki Script Service.

* Fix typo.