gateware.usb.request.windows: add MicrosoftOS10RequestHandler

[mndza]

This PR adds a request handler for Microsoft OS 1.0 descriptors.

greatscottgadgets/python-usb-protocol#41

Usage for a single interface:

Add OS string descriptor to the DeviceDescriptorCollection. The byte after MSFT100 defines the request value (bMS_VendorCode) for retrieving the OS descriptors:

descriptors.add_descriptor(get_string_descriptor("MSFT100\xee"), index=0xee)

Then add the request handler to the control endpoint:

msft_descriptors = MicrosoftOS10DescriptorCollection()

with msft_descriptors.ExtendedCompatIDDescriptor() as c:
    with c.Function() as f:
        f.bFirstInterfaceNumber = 0
        f.compatibleID          = 'WINUSB'
 
control_ep.add_request_handler(MicrosoftOS10RequestHandler(msft_descriptors, request_code=0xee))

NOTE: If LUNA complains about non-contiguous descriptors, you can pass avoid_blockram=True to the standard request handler as a temporary fix:

control_ep = usb.add_standard_control_endpoint(descriptors, avoid_blockram=True)

[mossmann]

Great work! I've marked this ready for review and am merging this so we can merge Cynthion #92..