Parsoid/Todo:Pre-save transforms

Tracked in 39160.

Much of the current parser's pre-save transform functionality can be moved to the editor, but there are also cases where this won't be possible. An example of the latter is the self-preserving en:Template:Selfsubst template.

Full pre-save transform functionality would be needed if we completely replaced the PHP parser with Parsoid and still support full wikitext editing. This would include:
 * Reverse pipe trick: We have implemented the regular pipe trick in the parser, so it should still render the same in HTML. The reverse pipe trick depends on the page title which would change with renames, so a save-time replacement seems to be needed to preserve.
 * The save parser section list in Markup_spec