Improve performance of line rendering.

- Create an overload that renders a line in one color, as this allows most existing calls to be simplified. This also allows a slight performance improvement by only normalizing the components once.
- Introduce a DrawLineStrip method. This improves performance by allowing the color components to be normalized once for the whole strip, and only needing to calculate vertices once per point rather than twice since we can reuse the last result.

OpenRA.Mods.Common/Widgets/ResourceBarWidget.cs

@@ -92,7 +92,7 @@ namespace OpenRA.Mods.Common.Widgets
 							top.Y -= 1;
 						}
 
-						Game.Renderer.LineRenderer.DrawLine(bottom, top, color, color);
+						Game.Renderer.LineRenderer.DrawLine(bottom, top, color);
 					}
 				}
 				else
@@ -122,7 +122,7 @@ namespace OpenRA.Mods.Common.Widgets
 							right.X -= 1;
 						}
 
-						Game.Renderer.LineRenderer.DrawLine(left, right, color, color);
+						Game.Renderer.LineRenderer.DrawLine(left, right, color);
 					}
 				}
 				else