api: add ActivationToken::{from,into}_raw

This is needed when passing and getting token from the IPC to activate
the window.

src/window.rs

@@ -1544,11 +1544,34 @@ impl Default for ImePurpose {
 /// [`Window`]: crate::window::Window
 #[derive(Debug, PartialEq, Eq, Clone, Hash)]
 pub struct ActivationToken {
-    pub(crate) _token: String,
+    pub(crate) token: String,
 }
 
 impl ActivationToken {
-    pub(crate) fn _new(_token: String) -> Self {
-        Self { _token }
+    /// Make an [`ActivationToken`] from a string.
+    ///
+    /// This method should be used to wrap tokens passed by side channels to your application, like
+    /// dbus.
+    ///
+    /// The validity of the token is ensured by the windowing system. Using the invalid token will
+    /// only result in the side effect of the operation involving it being ignored (e.g. window
+    /// won't get focused automatically), but won't yield any errors.
+    ///
+    /// To obtain a valid token, use
+    #[cfg_attr(any(x11_platform, wayland_platform, docsrs), doc = " [`request_activation_token`].")]
+    #[cfg_attr(
+        not(any(x11_platform, wayland_platform, docsrs)),
+        doc = " `request_activation_token`."
+    )]
+    ///
+    #[rustfmt::skip]
+    /// [`request_activation_token`]: crate::platform::startup_notify::WindowExtStartupNotify::request_activation_token
+    pub fn from_raw(token: String) -> Self {
+        Self { token }
+    }
+
+    /// Convert the token to its string representation to later pass via IPC.
+    pub fn into_raw(self) -> String {
+        self.token
     }
 }