The component watches for binding of the usb-fastboot-function driver, sends/receives fastboot packets and process fastboot commands.
To add this component to your build, append --with-base src/firmware/fastboot-usb to the fx set invocation.
Use ffx component run to launch this component into a restricted realm for development purposes:
$ ffx component run /core/ffx-laboratory:fastboot-usb fuchsia-pkg://fuchsia.com/fastboot-usb#meta/fastboot-usb.cm