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/InvalidSettings.cs

@@ -0,0 +1,10 @@
+using Spectre.Console.Cli;
+
+namespace Spectre.Console.Tests.Data
+{
+    public sealed class InvalidSettings : CommandSettings
+    {
+        [CommandOption("-f|--foo [BAR]")]
+        public string Value { get; set; }
+    }
+}