Can't print / export to PDF

[dmorneau]

Environment

• Elixir & Erlang/OTP versions (elixir --version): Elixir 1.14.0-dev, OTP-25.rc1
• Operating system: macOS
• How have you started Livebook (mix phx.server, livebook CLI, Docker, etc): mix phx.server
• Livebook version (use git rev-parse HEAD if running with mix): ca0128d
• Browsers that reproduce this bug (the more the merrier): Safari

Current behavior

It doesn't seem possible to print or export to PDF a LiveBook page. For instance in Safari I tried:

• Save as: when opening the resulting archive, LiveView hangs trying to connect, then it turns into an error page about the server being down.
• Print: only shows the first page, everything else is cut off
• Export to PDF: similar to print, but in landscape orientation

Expected behavior

It would be quite useful if there was a way to print / export to PDF. My use case was providing a handout after a presentation. I think the normal print command is really close to working, if only it didn't cut off after the first page. Something about LiveBook seems to make it confused about how long the contents is...

[josevalim]

Dup of #605.