These methods need to move to new corresponding methods in ContentHandler. Here's a patch that does the first part of the work for Content::preSaveTransform.
The signature of the ContentHandler method should be:
- ContentHandler::preloadTransform( Content, PageReference, ParserOptions, array )
- Do the same as in the referenced patch for all the methods.
- In all extensions where Content overriding classes override the method - override the ContentHandler method instead
- Replace all callers. Use ContentHandlerFactory to obtain a ContentHandler, not the Content::getContentHandler method
- Once all callers and overrides in extensions is done, do some hard deprecations.