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/MultiSelectionSample.cs

@@ -0,0 +1,40 @@
+using DocExampleGenerator;
+using Spectre.Console;
+
+namespace Generator.Commands.Samples
+{
+    internal class MultiSelectionSample : 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)
+        {
+            var favorites = console.Prompt(
+                new MultiSelectionPrompt<string>()
+                    .PageSize(10)
+                    .Title("What are your [green]favorite fruits[/]?")
+                    .MoreChoicesText("[grey](Move up and down to reveal more fruits)[/]")
+                    .InstructionsText("[grey](Press [blue]<space>[/] to toggle a fruit, [green]<enter>[/] to accept)[/]")
+                    .AddChoiceGroup("Berries", new[]
+                    {
+                        "Blackcurrant", "Blueberry", "Cloudberry",
+                        "Elderberry", "Honeyberry", "Mulberry"
+                    })
+                    .AddChoices(new[]
+                    {
+                        "Apple", "Apricot", "Avocado", "Banana",
+                        "Cherry", "Cocunut", "Date", "Dragonfruit", "Durian",
+                        "Egg plant",  "Fig", "Grape", "Guava",
+                        "Jackfruit", "Jambul", "Kiwano", "Kiwifruit", "Lime", "Lylo",
+                        "Lychee", "Melon", "Nectarine", "Orange", "Olive"
+                    }));
+
+            console.MarkupLine("Your selected: [yellow]{0}[/]", string.Join(',', favorites));
+        }
+    }
+}