[css-anchor-position-1] 各種更新

Add missing span-left/span-right values to definition
w3c/csswg-drafts@f1b21ac

editorial: Fix capitalization.
w3c/csswg-drafts@6a58dc9

Clarify when last successful position is cleared.
w3c/csswg-drafts@5326ee9

Rewrite valid anchor rules into a less confusing form.
w3c/csswg-drafts@184472e

Add 'dialog' alignment value.
w3c/csswg-drafts@bf9c26a

Author: triple-underscore