Migrate from LineBreakIteratorPool to TextBreakIteratorCache
<rdar://problem/110097890>
Pull request: https://github.com/WebKit/WebKit/pull/14573
Committed 264825@main (9ad6a13de3e5): <https://commits.webkit.org/264825@main> Reviewed commits have been landed. Closing PR #14573 and removing active labels.