Prettier would do this anyway, but it’s separated out for a more
reviewable diff. Generated by ESLint.
Signed-off-by: Anders Kaseorg <anders@zulip.com>
This starts the concept of a schema checker, similar to
zerver/lib/validator.py on the server. We can use this
to validate incoming data. Our server should filter most
of our incoming data, but it's useful to have client-side
checking to defend against things like upgrade
regressions (i.e. what if we change the name of the field
on the server side without updating all client uses).