The stack reads its own descriptors to figure out which endpoints
are used in which alt settings, and enables/disables them as needed.
The ControlHandler has a callback so it can get notified of alternate
setting changes, which is purely informative (it doesn't have to do anything).
The same API call allocates interfaces/endpoints/etc and writes their descriptors.
This means less API calls, and less possibility to screw things up.
DescriptorWriter is now private.
- Renamed structs to HidReaderWriter, HidReader, HidWriter.
- Removed unused const generics on `State`.
- Simplified generics on `HidReaderWriter`.
The class type previously was `HidClass<D, Driver<'d, USBD>, ReportReader<'d, Driver<'d, USBD>, OUT_N>, IN_N>`
It's now `HidClass<D, Driver<'d, USBD>, IN_N, OUT_N>`. Note that the driver type `Driver<'d, USBD>` is no longer repeated.
- Constructors are now: `HidWriter::new()` for IN-only, `HidReaderWriter::new()` for IN+OUT. No complicated bounds.
- HidReaderWriter has all the methods from HidReader, HidWriter.
