Add support for alternate screen buffers

Closes #250

src/Spectre.Console.Testing/Internal/NoopExclusivityMode.cs

@@ -10,7 +10,7 @@ namespace Spectre.Console.Testing
             return func();
         }
 
-        public async Task<T> Run<T>(Func<Task<T>> func)
+        public async Task<T> RunAsync<T>(Func<Task<T>> func)
         {
             return await func().ConfigureAwait(false);
         }

src/Spectre.Console.Testing/TestConsoleInput.cs

@@ -66,6 +66,12 @@ namespace Spectre.Console.Testing
             _input.Enqueue(new ConsoleKeyInfo((char)input, input, false, false, false));
         }
 
+        /// <inheritdoc/>
+        public bool IsKeyAvailable()
+        {
+            return _input.Count > 0;
+        }
+
         /// <inheritdoc/>
         public ConsoleKeyInfo? ReadKey(bool intercept)
         {