Surfacing MSD features via DAPLINK

[DavidWhaleMEF]

This is a holding ticket, because I couldn't find any visible activity tickets that captured this work, and PXT is reliant on this work in order to be able to surface a good filing system experience.

See PXT ticket: https://github.com/Microsoft/pxt/issues/1495 which requests a status update of MSD work.

[finneyj]

Thanks @DavidWhaleMEF

Agree, this is a key part of the experience. @jamesadevine worked up a prototype of this, but changes required to DAPLink are non-trivial, and given the nature of the technology, testing is very challenging as pretty much all host OS behave slightly differently. It maybe we could release a read-only version in the first instance - this would mitigate much of the complexity.

Doing this would still require:

• porting of James' prototype to the latest stable daplink version
• filtering it down to a read-only operation
• testing and integration of the JMX json parser
• agreement on if/how we handle persisting non-volatile config data across reflash operations
• a heap of testing of the new firmware on as many host os revisions as we can muster

Any takers?