Add automated test for "Save Fullscreen Editor"

The manual test is here: Save Fullscreen Editor

Existing automated coverage

• RealtimeWYSIWYGEditorIT#editFullScreen: Toggles Maximize in the standalone and in-place realtime editors, saves with Save & View from full screen (standalone) and Done (in-place); asserts the final view content of the in-place save.

Missing automated coverage

• After clicking Maximize, assert the editor is in full screen (maximize button on / cke_maximized), in standalone and in-place modes.
• Click Save & View from full screen in the standalone editor and assert the browser is on the view URL and the saved content is displayed.
• Also cover the non-realtime CKEditor (realtime disabled) Save & View from full screen.

Suggested location: xwiki-platform-core/xwiki-platform-ckeditor/xwiki-platform-ckeditor-test/xwiki-platform-ckeditor-test-docker/src/test/it/org/xwiki/ckeditor/test/ui/SaveIT.java

Found by comparing the XWiki 18.4.4 manual test runs against the automated tests on master (a0055f10a1a).