window: Add Ctrl+W shortcut for closing the window

Add the common shortcut as per:
https://developer.gnome.org/hig/reference/keyboard.html#basic-shortcuts

src/gui/gcal-window.blp

@@ -79,6 +79,11 @@ template $GcalWindow: Adw.ApplicationWindow {
       action: "action(win.new-event)";
     }
 
+    Shortcut {
+      trigger: "<Control>w";
+      action: "action(window.close)";
+    }
+
     Shortcut {
       trigger: "<Control>q";
       action: "action(app.quit)";

src/gui/shortcuts-dialog.blp

@@ -32,7 +32,7 @@ Adw.ShortcutsDialog shortcuts_dialog {
 
     Adw.ShortcutsItem {
       title: C_("shortcut dialog", "Close Window");
-      accelerator: "<Primary>Q";
+      accelerator: "<Primary>Q <Primary>W";
     }
 
     Adw.ShortcutsItem {