There are many new versions since the currently used 3.0.15: https://github.com/jackmoore/autosize/blob/master/changelog.md
It should also be moved to separate directory (e.g. libs) that is excluded from formatting changes like was done in https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Translate/+/503476
Change 520353 had a related patch set uploaded (by Dmattern; owner: Dmattern):
[mediawiki/extensions/Translate@master] Upgrade jquery.autosize
Not sure if there is a more standardized way of doing this but I pulled in the latest release using composer and had it copy the file out to the libs dir for use. I was hoping to not have to keep the actual file in the repository, but if this is not how it is done, or if there is a more correct way I'd be happy to modify it.