Add CSS border-shape

[Schweinepriester]

• Via
  • https://mastodon.social/@intenttoship.dev@bsky.brid.gy/116159598617949372
  • https://groups.google.com/a/chromium.org/g/blink-dev/c/zSuB_Tc0-bY/m/P_Ki7Z8iAQAJ
• Spec: https://drafts.csswg.org/css-borders-4/#border-shape
• Explainer: https://github.com/noamr/explainers/blob/main/border-shape-explainer.md
• Chrome
  • Shipping in 147
  • https://groups.google.com/a/chromium.org/g/blink-dev/c/zSuB_Tc0-bY/m/P_Ki7Z8iAQAJ
  • https://chromestatus.com/feature/5459864205393920
• Firefox
  • [css-borders-4] border-shape property mozilla/standards-positions#1365
• Safari
  • [css-borders-4] border-shape property WebKit/standards-positions#625

Summary
CSS border-shape enables creating non-rectangular borders, with any arbitrary shape (polygon, circle, shape(), etc). Though border-shape accepts the same shapes as clip-path, it is fundamentally different: border-shape defines the shape of the border, decorates it, and clips only the inside. border-shape has two variants: one variant that strokes a shape, and another variant that fills between two shapes.