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/DogSettings.cs

@@ -0,0 +1,23 @@
+using Spectre.Console.Cli;
+
+namespace Spectre.Console.Tests.Data
+{
+    public sealed class DogSettings : MammalSettings
+    {
+        [CommandArgument(0, "<AGE>")]
+        public int Age { get; set; }
+
+        [CommandOption("-g|--good-boy")]
+        public bool GoodBoy { get; set; }
+
+        public override ValidationResult Validate()
+        {
+            if (Name == "Tiger")
+            {
+                return ValidationResult.Error("Tiger is not a dog name!");
+            }
+
+            return ValidationResult.Success();
+        }
+    }
+}