Update WR (switch to new text-decorations API in WR).

This only makes use of the "Solid" text decoration type, which
matches the existing support. WR now supports dotted, dashed
and wavy text decorations, but supporting those will need some
extra work in Servo to pass through the correct values.

components/gfx/display_list/mod.rs

@@ -1146,7 +1146,8 @@ pub struct LineDisplayItem {
     pub color: ColorF,
 
     /// The line segment style.
-    pub style: border_style::T
+    #[ignore_heap_size_of = "enum type in webrender"]
+    pub style: webrender_api::LineStyle,
 }
 
 /// Paints a box shadow per CSS-BACKGROUNDS.