This is primarily for use on Linux to get by-id or by-path device names.
This information is now part of UsbCameraInfo.
A new entry point was added to UsbCamera to get that camera's UsbCameraInfo.
The alternate paths are also returned in EnumerateUsbCameras.
This avoids a number of shutdown use-after-free races by controlling the
destruction order. It also is a prerequisite to making the internal
interfaces mockable for unit testing.
