merge_pr_50510

CSS corner-shape initial parsing

See https://drafts.csswg.org/css-borders-4/#corner-shaping

This adds the flag, property definition (logical+physical), and
parsing a couple of the keywords.

It also adds the Superellipse style type for storage.

Note that the changes to the corner-shape syntax affect existing
WPTs, which don't currently pass in any browser.

ChromeStatus: https://chromestatus.com/feature/5357329815699456
I2P: https://groups.google.com/a/chromium.org/g/blink-dev/c/UKLLVghiHYQ/m/tv0ANlToEQAJ
Bug: 393145930
Change-Id: Ie31440e97f75f42dd4c8129cb34f6f0685884374
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6225742
Commit-Queue: Noam Rosenthal [email protected]
Reviewed-by: Fredrik Söderquist [email protected]
Cr-Commit-Position: refs/heads/main@{#1416146}