Updatte `codeblock-to-json.ts` to match new Quarto behaviour

[kv9898]

Also at quarto-ext/shinylive#65

In the current implementation, codeblock-to-json.ts uses:

import { readLines } from "https://deno.land/std/io/mod.ts";

Quarto 1.6 introduced breaking changes, which require an update in the code in favour of sth like:

import { readLines } from "stdlib/io";

[georgestagg]

As mentioned in the linked thread, this will require some thought to handle both the breaking change in Quarto and older versions. We might require two scripts and use the correct one based on quarto version.

[georgestagg]

My understanding is that this should now be working again in the latest Quarto builds.

We should leave this open for the moment, however, since it's possible Quarto might re-enable the use of --cached-only in the future and if so our script will break again.