Linux: StartupWMClass is the window's app id (#1087)

* Linux: StartupWMClass is the window's app id

The desktop entry said StartupWMClass=pdfcraft, but the window carries the
app id ai.storyteller.pdfcraft (APP_ID) on Wayland and under X11 alike, so
nothing that matches a window to its launcher by that key ever matched it:
on X11 the launch's startup notification can't end when the window maps.
VectorCraft, GridCraft and WordCraft already use the app id.

A test reads the entry and compares it with APP_ID.

* Contributors: add atoslins (Atos Lins)

---------

Co-authored-by: Brandon Thomas <echelon@gmail.com>

apps/pdfcraft/src/main.rs

@@ -1173,4 +1173,13 @@ mod tests {
         }
         let _ = std::fs::remove_dir_all(&dir);
     }
+
+    /// X11 startup notification and docks match a window to its launcher by `StartupWMClass`,
+    /// so it has to be the class the window carries: the app id, on Wayland and X11 alike.
+    #[test]
+    fn the_desktop_entry_names_the_window_class() {
+        let entry = include_str!("../../../packaging/linux/ai.storyteller.pdfcraft.desktop");
+        let class = entry.lines().find_map(|line| line.strip_prefix("StartupWMClass="));
+        assert_eq!(class, Some(super::APP_ID));
+    }
 }