Supersedes !7997
-- v2: windows.devices.enumeration: Implement initial device enumeration for DeviceWatcher::Start(). windows.devices.enumeration: Split setupapi device enumeration to a separate helper. windows.devices.enumeration: Implement EnumerationCompleted handler for DeviceWatcher. windows.devices.enumeration: Implement DeviceWatcher async state changes. windows.devices.enumeration: Implement DeviceWatcher::get_Status. windows.devices.enumeration: Factor DeviceWatcher creation in a device_watcher_create helper. windows.devices.enumeration: Implement IDeviceInformationStatics::CreateWatcher. windows.devices.enumeration: Add tests for initial device enumeration in DeviceWatcher.