2048: Make board size and target tile configurable

This adds a "settings" option that allows the user to configure the
board size and target tile, and optionally save them to a config file.
Closes #3219.

Games/2048/Game.h

@@ -30,7 +30,7 @@
 
 class Game final {
 public:
-    Game(size_t);
+    Game(size_t board_size, size_t target_tile = 0);
     Game(const Game&) = default;
 
     enum class MoveOutcome {
@@ -51,15 +51,26 @@ public:
 
     size_t score() const { return m_score; }
     size_t turns() const { return m_turns; }
+    u32 target_tile() const { return m_target_tile; }
+    u32 largest_tile() const;
 
     using Board = Vector<Vector<u32>>;
 
     const Board& board() const { return m_board; }
 
+    static size_t max_power_for_board(size_t size)
+    {
+        if (size >= 6)
+            return 31;
+
+        return size * size + 1;
+    }
+
 private:
     void add_random_tile();
 
     size_t m_grid_size { 0 };
+    u32 m_target_tile { 0 };
 
     Board m_board;
     size_t m_score { 0 };