Auto merge of #20294 - glennw:update-wr-blend-brush, r=jdm

Update WR (port blurs and blits to brush_image).

<!-- Reviewable:start -->
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/20294)
<!-- Reviewable:end -->