Support macos platform

[ekuleshov]

It looks like https://github.com/Polidea/RxBluetoothKit supports both iOS and OSX platforms.

Would it be possible to add support for macos in the FlutterBleLib. The code supposedly should be similar to what's there for iOS.

[mikolak]

I don't know much about either iOS or macOS. Since the only real dependency is Core Bluetooth, supported by both platforms, I'd imagine it possible to just use the iOS dependency and write only the bridging code, possibly reusing or linking most of the code from the iOS, as it's written in obj-c. Unfortunately my time for the library is severely limited, so unless I get a PR with it, it's gonna be the decision of the team that takes over.