[css-anchor-position] Support revert-(layer) in @position-try

@position-try rules cascade to a separate origin, which means both
revert and revert-layer in @position-try revert back to the author
origin.

Bug: 40281995
Change-Id: I08dac7005a6e79aa2a08fc9d8f63cb80a3e077a4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5376497


Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Reviewed-by: Anders Hartvoll Ruud <andruud@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1278839}