Add set_dock_visibility method to support setting the visibility of the application in the dock.
Close #105

As mentioned here, refer to Electron to implement set_dock_visibility method.

This is my first PR, so there are some issues that need further confirmation:

• Does the implementation of set_dock_visibility need to be completely consistent with set_activation_policy. For example, we don’t need to do anything extra here: https://github.com/1111mp/tao/blob/c4d0f0555fb0f65993fa4f7b944c45465ed14211/src/platform_impl/macos/app_delegate.rs#L32

  pub struct AuxDelegateState {
      /// We store this value in order to be able to defer setting the activation policy until
      /// after the app has finished launching. If the activation policy is set earlier, the
      /// menubar is initially unresponsive on macOS 10.15 for example.
      pub activation_policy: ActivationPolicy,
  
      /// Whether the application is visible in the dock.
      pub dock_visibility: bool,
  
      pub activate_ignoring_other_apps: bool,
  }

• Does the implementation of set_dock_show need to be exactly the same as Electron. At present, I am testing locally that the display and hiding of docker are consistent with the behavior of Electron. More extensive testing may be needed...

This is my local demo:

Should the icon change only occur in the local environment? I pointed tauri and tao directly to the local code by patch.crates-io and then started the demo project.

[patch.crates-io]
tauri = { path = "../../tauri/crates/tauri" }
tao = { path = "../../tao" }

Demo code:

// Learn more about Tauri commands at https://tauri.app/develop/calling-rust/
#[tauri::command]
fn greet(name: &str) -> String {
    format!("Hello, {}! You've been greeted from Rust!", name)
}

#[tauri::command]
fn set_dock_visibility(app_handle: tauri::AppHandle, visible: bool) {
    let _ = app_handle.set_dock_visibility(visible);
    // let _ = app_handle.set_dock_visibility(true);
    // let _ = app_handle.set_dock_visibility(false);
    // let _ = app_handle.set_dock_visibility(true);
    // let _ = app_handle.set_dock_visibility(false);
}

#[cfg_attr(mobile, tauri::mobile_entry_point)]
pub fn run() {
    let builder = tauri::Builder::default()
        .plugin(tauri_plugin_opener::init())
        .setup(|app| {
            // app.set_activation_policy(tauri::ActivationPolicy::Regular);
            // app.set_dock_visibility(false);
            Ok(())
        })
        .invoke_handler(tauri::generate_handler![greet, set_dock_visibility]);

    let app = builder.build(tauri::generate_context!()).unwrap();

    app.run(|app, err| match err {
        tauri::RunEvent::ExitRequested { api, .. } => {
            api.prevent_exit();
            let _ = app.set_dock_visibility(false);
        }
        _ => {}
    });
}

This is my first time to submit a PR. If I have any mistakes, please feel free to correct me. Thank you.