Allow omitting for anchor-size()
The anchor-size implicitly follow the property to which it is applied.
Split the kSize evaluator mode into kWidth/kHeight to map an implicit
to the right axis.
Bug: 343516786
Change-Id: I698139f91fd976282cb6ffa15065ed2ec9eef467
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5824430
Commit-Queue: Rune Lillesveen futhark@chromium.org
Reviewed-by: Anders Hartvoll Ruud andruud@chromium.org
Cr-Commit-Position: refs/heads/main@{#1348587}