Moved analyzer tests to its own project

Also moves tests to `./test` which makes it possible
for all test projects to share the same .editorconfig
files and similar.

test/Spectre.Console.Tests/Data/Settings/CatSettings.cs

@@ -0,0 +1,15 @@
+using System.ComponentModel;
+using Spectre.Console.Cli;
+
+namespace Spectre.Console.Tests.Data
+{
+    public class CatSettings : MammalSettings
+    {
+        [CommandOption("--agility <VALUE>")]
+        [TypeConverter(typeof(CatAgilityConverter))]
+        [DefaultValue(10)]
+        [Description("The agility between 0 and 100.")]
+        [PositiveNumberValidator("Agility cannot be negative.")]
+        public int Agility { get; set; }
+    }
+}