Syntax change is not propagated by the realtime editing session

Follow these steps to reproduce:

• edit a page in standalone WYSIWYG mode
• duplicate the browser tab, in order to simulate multiple users editing the same page
• change the document syntax from the first tab and confirm the syntax conversion => the editor is reloaded and reconnected to the realtime session
• switch to the second browser tab and check the document syntax => you still have the old syntax

This means that:

• a syntax change in a realtime session is quickly "reverted" when others make changes
• since the edited content can contain wiki syntax in HTML comments (rendering markers) this can cause problems to the realtime sync and also problems on save when content written in syntax A is saved as is on a document with syntax B, and thus is not properly rendered on view
• each syntax can have types of styles / blocks that are not supported; for this reason we configure the WYSIWYG editor to disable the features that produce those styles / blocks; if the syntax change is not propagated when the other users will be able to produce content that can't be saved with the new syntax, and thus will be lost or cause problems on save

We need to include the document syntax in the information that is synchronized by realtime, and we also need to handle a remote syntax change by reloading the WYSIWYG editor for all the participants in the realtime session, in order to use the new "schema" (content filter) that prevents users from producing content (HTML) that can't be saved in the new syntax.