A lot of USB structures contain back pointers to their parents,
so we need to be careful about how we copy them around, and update
the back pointers as necessary.
This fixes incorrect assumptions about the layout of descriptors and
gets rid of all the pointer arithmetic.
The USB spec doesn't define a strict order for all descriptors to appear
in.
It just says that endpoint descriptors follow its interface descriptor.
We also have to skip all unknown descriptors (which also can appear
anywhere), not just HID descriptors.
This creates all interfaces when the device is enumerated, with a link
to the configuration that it is a part of. As such, a new class,
`USBInterface` has been introduced to express this state.
