Add automated test for "In-line macro content editing"

Note: org.xwiki.ckeditor.test.ui.MacroIT, listed above as existing coverage, is not nested in the module AllIT. The failsafe configuration only runs **/AllIT.java, so this class does not run on CI and that coverage is not exercised. When adding the missing test, also nest MacroIT in AllIT (and fix it if it fails), otherwise the new test won't run either.