Closer implementation of webBluetooth API

[derwehr]

In order to closer follow method signatures of the web bluetooth API, i propose the following changes:

• argument of writeValue, writeValueWithResponse and writeValueWithoutResponse should be of type BufferSource
• return type of readValue should be Promise<DataView>

This would make it easier to switch between web and node implementations.
I could implement this if you're interested in merging.