Add microbit firmata (1)

[epeach]

Description

This adds this microbit firmata to our third-party code folder: https://github.com/microbit-foundation/microbit-firmata

It includes the changes that are pending in this PR: microbit-foundation/microbit-firmata#3

There are eventual plans to reference this code from the package.json once that^ PR has been accepted and after the demo.

Reviewer Checklist:

• Tests provide adequate coverage
• Code is well-commented
• New features are translatable or updates will not break translations
• Relevant documentation has been added or updated
• User impact is well-understood and desirable
• Pull Request is labeled appropriately
• Follow-up work items (including potential tech debt) are tracked and linked

cc: @joshlory