Adapter: registerBluetoothConnection

Registering the callback is done in two step, the API should return true
as long as it managed to add the callback to its list.
Registering the callback to the Bluetooth service is done anytime the
bluetooth is up

Bug: 339585576
Bug: 341846395
Flag: Exempt fixing test flakiness
Test: atest CtsBluetoothTestCases
Change-Id: Ibced64d8901456f925b154aff3620810ddab2e3c