[css-color-hdr] Add mechanism to query HDR headroom

[mozilla-apprentice]

A resolution was made for csswg-drafts/#9306.

[css-color-hdr] Add mechanism to query HDR headroom

• RESOLVED: CSS WG adopts the CSS Color HDR draft as a work item

Discussion.

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To file a bug automatically for these resolutions, add the bug label to the issue.

If no bug is needed, the issue can be closed.

[dholbert]

Looks like this was just agreeing to adopt the draft spec, which we have tracked in metabug https://bugzilla.mozilla.org/show_bug.cgi?id=1954795 . --> no bug needed at this point.