Better live docs

[fonsp]

New discussion page

We created https://github.com/JuliaCommunity/live-docs-discussion/discussions as a dedicated place to discuss Pluto's Live Docs feature, and future ideas for Julia's documentation in general! Take a look!

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Some improvements:

• [x] Show what is currently being searched for
• [x] Support cross-reference links between docs
• [ ] Show that it is searching
• [x] Title of the docs should be a textbox where you can enter a query directly
• [x] Handle dots, like Module.funky
• [ ] Function arguments
• [ ] Show when the name is found but it has no docs
• [ ] To the right of a cell might make more sense
• [ ] Heuristics for which function is dispatched on - can VS Code do this nowadays? I guess that we can do this dynamically, since some of the types are known
• [ ] https://github.com/fonsp/Pluto.jl/issues/832#issuecomment-758270561
• [ ] https://github.com/fonsp/Pluto.jl/issues/832#issuecomment-758271508

Extras:

• [ ] apropos(str) might be useful. Is resource intensive though, maybe write our own version that just returns the first hit? Although that might not be the most relevant one
• [ ] Show filename and line number of defintion. Double cool if it is a clickable link to GitHub! (Like in methodtables shown as text/html) I found this useful when the docs are unclear or when you want to know how something works.

What is Julia's doc system missing? CLIPPY

• [ ] Given an object, tell you what you can do with it. In OOP languages this is obj.<TAB> to autocomplete.

Please post other ideas and suggestions!