The `start-local-collaboration` script opens two instances of Zed, each
logged in as a different user, and each one taking up half of the
screen. But previously, when joining a remote project as one of the
collaborators, that newly-opened window would be full screen.

Now, each instance of Zed keeps *all* of its windows on its half of the
screen. This is implemented by respecting the `ZED_WINDOW_{SIZE,BOUNDS}`
env vars, even when joining *remote* projects.

Release Notes:

- N/A