Add support for fake input in asciicast recordings

* Fixes a bug with `SelectionPrompt` and page size.
* Allow `IAnsiConsoleInput` to return `null`.

resources/scripts/Generator/Commands/AsciiCast/Samples/SelectionSample.cs

@@ -0,0 +1,29 @@
+using DocExampleGenerator;
+using Spectre.Console;
+
+namespace Generator.Commands.Samples
+{
+    internal class SelectionSample : BaseSample
+    {
+        public override (int Cols, int Rows) ConsoleSize => (base.ConsoleSize.Cols, 14);
+
+        public override void Run(IAnsiConsole console)
+        {
+            console.DisplayThenType(AskFruit, "↓↓↓¦¦¦¦ ");
+        }
+
+        private static void AskFruit(IAnsiConsole console)
+        {
+            // Ask for the user's favorite fruit
+            var fruit = console.Prompt(
+                new SelectionPrompt<string>()
+                    .Title("What's your [green]favorite fruit[/]?")
+                    .PageSize(10)
+                    .MoreChoicesText("[grey](Move up and down to reveal more fruits)[/]")
+                    .AddChoices(new [] {"Apple", "Apricot", "Avocado", "Banana", "Blackcurrant", "Blueberry", "Cherry", "Cloudberry", "Cocunut"}));
+
+            // Echo the fruit back to the terminal
+            console.WriteLine($"I agree. {fruit} is tasty!");
+        }
+    }
+}