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>
We ignore keystrokes like alt-left-arrow and alt-right-arrow,
so that the browser can do back/forward.
We may need to refine the handling of ctrl/alt/shift in the
future, but now we only support single-key operations.