Summary:
- Using a sample of data was causing poor detection if the sample were
cut mid-character. Switch to using line-based detection.
- Add a simple option for changing encoding. No convenient UI is offered
since config UI is auto-generated, but this at least makes it possible to
recover from bad guesses.
- Upgrades chardet library for good measure.
- Also fixes python3-building step, to more reliably rebuild Python
dependencies when requirements3.* files change.
Test Plan:
Added a python-side test case, and a browser test that encodings can
be switched, errors are displayed, and wrong encodings fail recoverably.
Reviewers: alexmojaki
Reviewed By: alexmojaki
Differential Revision: https://phab.getgrist.com/D3979
