Reduce size of RenderText from 128 to 120 bytes on 64-bit by leveraging Markable.
Pull request: https://github.com/WebKit/WebKit/pull/18648
Committed 268887@main (728c278f5744): <https://commits.webkit.org/268887@main> Reviewed commits have been landed. Closing PR #18648 and removing active labels.
<rdar://problem/116497595>