feat(rosetta): expose the 'extract' API

[rix0rrr]

Expose parts of the extract API (cache reading and mass translating)
to consumers, so that downstream tools can build example manipulators
as well.

• The original exposed Rosetta class is renamed to RosettaTabletReader, and is intended to be used by pacmak (or tools that primarily read tablets).
• A new class is introduced, RosettaTranslator, which is intended to be used by tools that need to do mass translation. This new API exposes the worker-based caching and translateAll functionality.
• The extract command is rewritten to use RosettaTranslator
• The translateAll features are moved from extract.ts and extract_worker.ts to translate_all.ts and translate_all_worker.ts.
• Add a function to build a snippet from source with /// !show|!hide directives, make it clear when each is supposed to be used.
• Fix the console.error() suppression from the TypeScript compiler that was using an incorrect substring.

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[mergify]

Thank you for contributing! ❤️ I will now look into making sure the PR is up-to-date, then proceed to try and merge it!

[mergify]

Merging (with squash)...