Auto merge of #16398 - glennw:update-wr-elliptical-borders-aa, r=mrobinson

Update WR (new border code path).

This includes the new border code path for simple (solid) borders.
This gives much higher quality border rendering, including proper
support for elliptical border segments.

The quality on https://github.com/servo/servo is noticeably improved.

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components/layout/webrender_helpers.rs

@@ -275,7 +275,7 @@ impl WebRenderDisplayItemConverter for DisplayItem {
                     let clip = item.base.clip.to_clip_region(builder);
                     builder.push_text(item.base.bounds.to_rectf(),
                                       clip,
-                                      glyphs,
+                                      &glyphs,
                                       item.text_run.font_key,
                                       item.text_color,
                                       item.text_run.actual_pt_size,