It just confuses DolphinBar users and isn't relevant these days now that Windows users do not use alternative Bluetooth stacks.

Separate LibUSB logic into LibUSBBluetoothAdapter class.
Submit transfers on thread with proper timing.
Throttle before ACL input for reduced input latency.
Immediately send IPC replies for outgoing data.
Continuously submit libusb transfers to fill HCI/ACL input queues.
Simplify endpoint handling and state saving.
Other cleanups.

Fix the UI hanging for several seconds when opening the Controllers
window.

Move the scan for Bluetooth adapters onto a separate thread so the Host
thread doesn't have to wait for it.

Only automatically scan for adapters once, when opening the Controllers
window for the first time. Add a Refresh button to let the user refresh
the adapter list afterward.

SPDX standardizes how source code conveys its copyright and licensing
information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX
tags are adopted in many large projects, including things like the Linux
kernel.