Accurate device state detection for devices in DFU

[keeramis]

Problem

Currently, there is no way to distinguish between Open and Protected Devices in Service Mode when the device is in DFU mode.

Solution

This PR obtains and parses the result of the string descriptor with the correct index for the device state
Device-OS changes are in this PR (estimated 6.1.2)

Testing

Use this Device-OS PR -
Use a script like this

#!/usr/bin/env node

const { getDevices } = require('/path/to/particle-usb');

async function run() {
  let dev;
  try {
    // Open the first found USB device
    const devs = await getDevices();
    if (!devs.length) {
      throw new Error('No devices found');
    }
    dev = devs[0];
    if (!dev.isInDfuMode) {
      throw new Error('Device is not in DFU mode');
    }
    await dev.open();
    const res = await dev.getProtectionState();
    console.log('Protection state:', res);

  } catch (err) {
    console.error(err);
    process.exit(1);
  } finally {
    if (dev) {
      await dev.close();
    }
  }
}

run();

[monkbroc]

Looks great!