R session background connections

In #394, notebook.R runs a socket connection that the notebook communicates with. Would it be worth extracting part of this out so that a socket connection is available for each R session started by the user? This would make the following possible:

• Sending VS Code's R commands to the session invisibly, rather than having to send them as text to the console
• Querying the session, for example to get the names of data frames
• For Run Selection/Line, potentially using R instead of TypeScript to choose which lines to send (allowing use of R's parse functions)
• Inline evaluation (sending user code to the session invisibly, and displaying the results in the editor) - this one's not really necessary but some other languages/IDE's have it and it's kind of cool

@renkun-ken You wrote notebook.R and the session watcher, which has some overlap with this proposal, so you're definitely the best person to comment. Does this sound practical? Let me know if I need to clarify anything.

Inizia leggendo notebook.R e il lavoro su session watcher a cui si fa riferimento in #394, quindi esamina i casi d’uso proposti per i socket per sessione. L’issue richiede un ambito definito e una progettazione pratica prima che possa iniziare l’implementazione; sarebbe considerata completata quando fosse stato concordato un approccio per le connessioni di sessione e i comandi supportati da esse.