Update scanAttributeName::scanAttributeName() to return a QualifiedName instead of a `Span<const CharacterType>`. This simplifies the code a bit and is performance-neutral on Speedometer.
Pull request: https://github.com/WebKit/WebKit/pull/12863
Committed 263091@main (b0645e5bf688): <https://commits.webkit.org/263091@main> Reviewed commits have been landed. Closing PR #12863 and removing active labels.
<rdar://problem/108214461>