After change 790467, BagOStuff value segmentation only works on strings. The value segmentation, however, exists only for use by PageEditStash, and PageEditStash was not updated to serialize the ParserOutput/Content to strings first. Thus effectively disabling value segmentation and no longer storing applying edit stash optimisations to edits with a large ParserOutput object, which was fixed for T204742: Unable to store parser output in StashEdit (Memcached error: ITEM TOO BIG).
Ideally, this would use JSON where possible.
(Spun off from T309126.)
