Both CustomElementQueue and CustomElementReactionQueue always contain at least one item whenever they're created. Give them inline capacity to avoid malloc.
https://github.com/WebKit/WebKit/pull/15588
Committed 265829@main (9b42484b8e81): <https://commits.webkit.org/265829@main> Reviewed commits have been landed. Closing PR #15588 and removing active labels.
<rdar://problem/111877419>