Copy LAST_JEDI_COMPLETIONS to cell document so that completionItem/resolve will work

[hjr265]

Let's say I am running this LSP server with Ruff (for linting) and Jedi (for autocompletion, with eager off). I then open a notebook document with a few cells in it.

I open the document (and the cells) with the notebookDocument/didOpen method.

Now, I request completion using the method textDocument/completion and receive the completion items as expected.

So far, so good.

Now, if I attempt to resolve one of the completion items using the completionItem/resolve method, I receive an empty array as a result.

This issue occurs because PyLSP concatenates cells of notebook documents into a temporary document and then uses it to generate completion items. That temporary document has a "randomly" generated UUID as its URI. When generating completion items, the shared data "LAST_JEDI_COMPLETIONS" is stored on this temporary document.

However, when the client sends back any "completion item" to be resolved, it looks for "LAST_JEDI_COMPLETIONS" shared data on the actual cell document, where this shared data is not present, and the request to "resolve" fails.

This PR copies the "LAST_JEDI_COMPLETIONS" shared data from the temporary document to the cell document at the end of the "completion" request.