[WIP] QR commands for FujiNet device

[nwah]

⚠️ WIP - NOT READY FOR MERGE ⚠️

Could use help on how to set things up nicely as shared library all platforms call, with some platform-specific implementations. Will probably still just be Atari for now as I don't have hardware/software to test other platforms.

Will squash everything into 1 commit when ready.

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Adds new serial command(s) to the Fuji device for generating QR codes.

It follows the same pattern as base64/hash commands:

1. Send text to FN to be encoded, which is stored in a buffer
2. Tell FN to encode it. (For the QR code stuff you can specify version (size), and error correction level. The result is stored as bytes in a buffer.)
3. Ask the FN for the length in bytes of the result
4. Read bytes from the FN

Three output modes available: bytes (1 0x00 or 0x01 per QR "module"), bits (1 bit per module), or ATASCII (each char represents 2x2 chunk of the QR code).

[tschak909]

Thank you!