lsp/jupyter: support context across blocks

[kitsonk]

In jupyter notebooks, the context is shared across all the code blocks, though the language server appears to evaluating the context just within the current block, while the kernel is actually using the wider context.

For example if I declare something like this in a code block:

const VALUE = "hello";

I can use it in a subsequent code block:

console.log(VALUE);

But the LSP gives back:

Cannot find name 'VALUE' - deno-ts(2304)

But the code executes perfectly fine.

[sigmaSd]

#25423

[dsherret]

I really want this too. Let's track in denoland/vscode_deno#932 and #21709