Add a const OCTAGON and use it in map.rs

We could made a bunch of pre-built Card constatns for all the basic
shapes. That way we can `Card::OCTAGON` to create one, instead of typing
out the whole function call.

src/card.rs

@@ -97,6 +97,9 @@ impl Card {
     }
   }
 
+  // TODO: The other shapes
+  pub const OCTAGON: Self = Self::new(OCTAGON);
+
   /// Produces a new card by stacking another on top of this one.
   pub fn merge(self, top: Self) -> (Self, Option<Self>) {
     let mut new_card = Self::default();

src/game/map.rs

@@ -11,20 +11,7 @@ pub fn setup_test_tilemap(mut commands: Commands, assets: Res<AssetLibrary>) {
   let map_size = TilemapSize { x: 9, y: 9 };
   let mut tile_storage = TileStorage::empty(map_size);
 
-  let card = Card {
-    cells: [
-      Cell::NW,
-      Cell::Filled,
-      Cell::NE,
-      Cell::Filled,
-      Cell::Filled,
-      Cell::Filled,
-      Cell::SW,
-      Cell::Filled,
-      Cell::SE,
-    ],
-    ..Default::default()
-  };
+  let card = Card::OCTAGON;
 
   add_card_to_tilemap(
     &card,