This is necessary to get a library version after the write instead of an
item version. Otherwise after a full-text write, the main library
version is behind, so the next sync checks all object types for that
library instead of getting a 304.
Full text is batched up to 500K characters or 10 items, whichever is
less.
This also switches to using ?format=versions for /fulltext requests,
which isn't currently necessary but reflects what it's actually doing.
If a version is returned for an item's full-text content but a 404 is returned
for the content itself (because it's missing in Elasticsearch for some reason),
don't throw an error.
Also remove legacy array comprehensions in fulltext and syncFullTextEngine test
files, which apparently weren't being run.
