[NXT - help wanted]: WebUSB firmware installation

[laurensvalk]

pybricksdev has an implementation for flashing the NXT, but we don't have one for Pybricks Code yet.

The user experience would be similar to the recent addition of EV3 flash support.

Let's start by assuming that the user puts the brick in update mode, just like we do everywhere else.

Do we need any winusb drivers here like we do for DFU on SPIKE? If so, we should add instructions for this too in the same way.