GattServer: App exception aren't from SystemServer

Calling into mService(IBluetoothGatt) will call the GattService from
Bluetooth app that does not live in the systemServer.
Therefore, exception should be rethrown as runtimeException

Bug: 298264617
Test: atest CtsBluetoothTestCases | Cts does not handled failure in the
      binder nor any of the Test framework we currently have
Change-Id: Ia75654e3d5a6060a72d4031499ac98f8c89da697