Currently the setCollapsibleSections parser option splits the parser cache, which means that mobile content is stored in the parser cache twice, despite the section collapsing being a post-processing transformation.

As part of T348255's work to refine the ParserCache mechanism, we should introduce a ParserOptions type for "propagated to ParserOutput but not otherwise affecting the parse". These options would be omitted from the ParserCache key, but when a ParserOutput is retrieved based on the modified key is needs to be "fixed up" by propagating the *actual* ParserOptions to the ParserOutput using setFromParserOptions in a way which also overwrites any of that metadata left over from the original parse. (Or the original parse should always have the options wiped, so that the ParserOutput is a clean slate that we can naively run ParserOutput::setFromParserOptions on -- the problematic case is the output class wrapper, since ParserOutput::addWrapperDivClass will *append* a class to the one from the preview parse instead of overwriting it).

For example, a parse with 'wrap output class' set to foo should get parsed and stored as normal, but with wrap output class omitted from the ParserOptions and therefore result in a ParserOutput with an empty wrapper div class set, which is what is stored in the cache. ParserOutput::setFromParserOptions() is then called to transfer the 'foo' class to the ParserOutput before it is returned from ParserOutputAccess.

Then a subsequent parse with wrap output class set to bar would get 'wrap output class' omitted from the cache key and so could return the previously-rendered ParserOutput with an empty wrapper div class. Again, ParserOutput::setFromParserOptions() would be set on the ParserOutput fetched from the cache to transfer the 'bar' class to the ParserOutput before ParserOutputAccess returns.