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/Commands/InvalidCommand.cs

@@ -0,0 +1,12 @@
+using Spectre.Console.Cli;
+
+namespace Spectre.Console.Tests.Data
+{
+    public sealed class InvalidCommand : Command<InvalidSettings>
+    {
+        public override int Execute(CommandContext context, InvalidSettings settings)
+        {
+            return 0;
+        }
+    }
+}