Add SDL2 renderer based on SDL2# wrapper. Closes #3315.

SDL2# binary was built from commit 70af91f84493a924a3c1da46ae6209bb5f7222e3.

OpenRA.Renderer.Gl/GraphicsDevice.cs

@@ -39,6 +39,6 @@ namespace OpenRA.Renderer.Glsl
 		public GraphicsDevice(Size size, WindowMode window)
 			: base(size, window, requiredExtensions) { }
 
-		public override IShader CreateShader(string name) { return new Shader(this, name); }
+		public override IShader CreateShader(string name) { return new Shader(name); }
 	}
 }

OpenRA.Renderer.Gl/Shader.cs

@@ -25,7 +25,7 @@ namespace OpenRA.Renderer.Glsl
 		readonly Dictionary<int, ITexture> textures = new Dictionary<int, ITexture>();
 		int program;
 
-		public Shader(GraphicsDevice dev, string name)
+		public Shader(string name)
 		{
 			// Vertex shader
 			string vertexCode;