Use the rich text area page object to run quick actions in the CKEditor functional tests

Functional tests using CKEditor quick actions (slash commands) hand-code the same sequence each time: type the query, create an AutocompleteDropdown, waitForItemSelected(), press Enter, waitForItemSubmitted(), and then, for a macro, wait for the content to be re-rendered (often implicitly, by re-creating the rich text area page object with editor.getRichTextArea()).

The tests should use the RichTextAreaElement APIs added in XWIKI-25221 instead (executeQuickAction(), insertMacro(), insertMacroWithRequiredParameters()), so that the waits are done by the page objects.