Update value keywords for CSS position-area following CSS WG resolution

[jfkthame]

Test List

Tests in css/css-anchor/position:

position-area-align-justify-wm-dir.html
position-area-basic.html
position-area-computed.html
position-area-in-position-try.html
position-area-parsing.html
position-area-wm-dir.html
try-tactic-position-area.html

(Also affected, but not in interop-2025: anchor-center-visibility-change.html)

Rationale

The CSS WG recently resolved to rename a group (8 altogether) of the value keywords for position-area for better clarity/consistency.

(As these values are only just now being implemented, no webcompat problems are expected.)

[foolip]

@mfreed7 @lilles can either of you review this for Chromium?

@fantasai can you review this for WebKit? (suggseted by @stubbornella)

[nt1m]

Looks good from our side! (@fantasai gave a thumbs up to this issue)

[mfreed7]

@mfreed7 @lilles can either of you review this for Chromium?

I think we're ok with the renames of these, but this is just an issue right? I.e. is there a corresponding WPT PR to actually rename within the tests?

[nt1m]

@mfreed7 there's a PR here: web-platform-tests/wpt#55216

[mfreed7]

@mfreed7 there's a PR here: web-platform-tests/wpt#55216

Thanks! LGTM.