Display.published_to_js

[fonsp]

To expose fonsp/Pluto.jl#1124

I changed the name from publish_to_js to published_to_js to make it clear that this is declarative: calling the function on its own has no effect, data is only published when interpolating this into a script.

TODO:

• docs
• document how msgpack transforms types
• document caching
• matching Pluto PR Make publish_to_js official API through AbstractPlutoDingetjes fonsp/Pluto.jl#2162
• better error message when not rendered inside Pluto
• allow specifying a fallback? can be added later upon request?
• maybe add tricks to support older versions of Pluto?

[fonsp]

Replaced by #11