Support BLE MIDI Natively

[JonLatane]

Currently, you must use other apps on MacOS, iOS, and Android to connect a BLE MIDI controller to the system MIDI bus and use it. Since there are no in-OS apps for these platforms that do that, BeatScratch should integrate connecting to BLE MIDI controllers from the MIDI Settings pane.

Essentially:

1. Define the proto models for BLE MIDI and methods in BeatScratchPlugin. Set a flag for supportsBLE in BeatScratchPlugin.
2. Implement the UI for what available/connected BLE MIDI controllers look like in BeatScratch, using dummy BeatScratchPlugin results.
3. Implement the BeatScratchPlugin calls in Swift and Kotlin for macOS+iOS and Android.