Implement realloc function for Arena

mem/include/arena/mem_arena.h

@@ -13,6 +13,9 @@ typedef struct growing_arena Arena;
 bool wapp_mem_arena_init(Arena **arena, u64 base_capacity);
 void *wapp_mem_arena_alloc(Arena *arena, u64 size);
 void *wapp_mem_arena_alloc_aligned(Arena *arena, u64 size, u64 alignment);
+void *wapp_mem_arena_realloc(Arena *arena, void *ptr, u64 size);
+void *wapp_mem_arena_realloc_aligned(Arena *arena, void *ptr, u64 size,
+                                     u64 alignment);
 void wapp_mem_arena_clear(Arena *arena);
 void wapp_mem_arena_free(Arena **arena);