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/Unit/Progress/ProgressColumnFixture.cs

@@ -0,0 +1,28 @@
+using System;
+using Spectre.Console.Rendering;
+using Spectre.Console.Testing;
+
+namespace Spectre.Console.Tests.Unit
+{
+    public sealed class ProgressColumnFixture<T>
+        where T : ProgressColumn, new()
+    {
+        public T Column { get; }
+        public ProgressTask Task { get; set; }
+
+        public ProgressColumnFixture(double completed, double total)
+        {
+            Column = new T();
+            Task = new ProgressTask(1, "Foo", total);
+            Task.Increment(completed);
+        }
+
+        public string Render()
+        {
+            var console = new TestConsole();
+            var context = new RenderContext(console.Profile.Capabilities);
+            console.Write(Column.Render(context, Task, TimeSpan.Zero));
+            return console.Output;
+        }
+    }
+}