Summary:
Adds a Python function `REQUEST` which makes an HTTP GET request. Behind the scenes it:
- Raises a special exception to stop trying to evaluate the current cell and just keep the existing value.
- Notes the request arguments which will be returned by `apply_user_actions`.
- Makes the actual request in NodeJS, which sends back the raw response data in a new action `RespondToRequests` which reevaluates the cell(s) that made the request.
- Wraps the response data in a class which mimics the `Response` class of the `requests` library.
In certain cases, this asynchronous flow doesn't work and the sandbox will instead synchronously call an exported JS method:
- When reevaluating a single cell to get a formula error, the request is made synchronously.
- When a formula makes multiple requests, the earlier responses are retrieved synchronously from files which store responses as long as needed to complete evaluating formulas. See https://grist.slack.com/archives/CL1LQ8AT0/p1653399747810139
Test Plan: Added Python and nbrowser tests.
Reviewers: georgegevoian
Reviewed By: georgegevoian
Subscribers: paulfitz, dsagal
Differential Revision: https://phab.getgrist.com/D3429
