Change IAnsiConsole to render IRenderable

This makes it possible for encoders to output better representation
of the actual objects instead of working with chopped up segments.

* IAnsiConsole.Write now takes an IRenderable instead of segments
* Calculating cell width does no longer require a render context
* Removed RenderContext.LegacyConsole
* Removed RenderContext.Encoding
* Added Capabilities.Unicode

src/Spectre.Console/Extensions/RecorderExtensions.cs

@@ -1,4 +1,5 @@
 using System;
+using Spectre.Console.Internal;
 
 namespace Spectre.Console
 {