Use Web Serial polyfill to add Android support

[paulstraw]

Is your feature request related to a problem? Please describe.
pdportal doesn't currently support any mobile devices, because it requires Web Serial.

Describe the solution you'd like
As mentioned by dlog in this thread, there's a Serial API Polyfill available from Google that implements Web Serial on top of WebUSB. The polyfill repo explicitly mentions Android support. See also, https://caniuse.com/webusb

Describe alternatives you've considered
None

Additional context
I'd like to wait to action this until 0.2.0 lands.