Windows service improvements for hosting, testing, fallback, and extended commands

[kennykerr]

This update provides a major overhaul of the windows-services crate and addresses a number of issues to support more scenarios and features while retaining the simplicity of the Service builder by default.

• Provides the foundation for supporting extended controls by switching from RegisterServiceCtrlHandlerW to RegisterServiceCtrlHandlerExW internally.
• Provides a new Extended variant for the Command enum to allow services to receive extended control information.
• Provides a new can_accept builder method to specify other specific commands to accept.
• Provides a new can_fallback builder method to allow the service to provide specific handling when the service is not started by the Service Control Manager.
• The run method is no longer fatal so that a caller may decide to gracefully handle and detect when the service is not started by the Service Control Manager.
• Provides a new handle method to retrieve the handle representing the service. This may be used to call other service-related functions like RegisterPowerSettingNotification.

Additional samples and tests are now provided thanks to the greater flexibility afforded by the new implementation.

Fixes: #3610
Fixes: #3641

[edvard-pettersen-elas-ai]

@kennykerr, the API looks good, but there are some additional steps that are required to support SERVICE_CONTROL_POWEREVENT. After having specified can_accept(SERVICE_ACCEPT_POWEREVENT), the application also needs to specify which power events to register for notification by calling RegisterPowerSettingNotification. This requires access to the handle returned by RegisterServiceCtrlHandlerExW, which doesn't seem accessible in the current proposal.

[kennykerr]

37c0d93 adds a handle method that you can use to retrieve the service handle. You might for example use it when responding to Command::Start to call RegisterPowerSettingNotification. Something like this:

let mut power_handle = 0;

Service::new()
    .can_stop()
    .can_accept(SERVICE_ACCEPT_POWEREVENT)
    .run(|service, command| {
        if command == Command::Start {
            power_handle = unsafe {
                RegisterPowerSettingNotification(
                    service.handle(),
                    &GUID_GLOBAL_USER_PRESENCE,
                    DEVICE_NOTIFY_SERVICE_HANDLE,
                )
            };
        }

        if let Command::Extended(command) = command {
            if command.control == SERVICE_CONTROL_POWEREVENT {
                debug_assert!(command.ty == PBT_POWERSETTINGCHANGE);
                let data = unsafe { &*(command.data as *const POWERBROADCAST_SETTING) };
                debug_assert!(&data.PowerSetting == &GUID_GLOBAL_USER_PRESENCE);
                debug_assert!(data.DataLength == 4);

                let data = unsafe {
                    std::slice::from_raw_parts(data.Data.as_ptr(), data.DataLength as usize)
                };

                let data = u32::from_le_bytes(data.try_into().unwrap());
                writeln!(log, "Present: {data}").unwrap();
            }
        }
    })
    .unwrap();