This legacy inline box bit is used to set directionOverride bit when creating a TextRun for the box. However that bit is never needed in cases these TextRuns are created for (painting and editing). In practice it only affects render tree dumps and can be removed.
Created attachment 444965 [details] Patch
Created attachment 444967 [details] Patch
Created attachment 444972 [details] Patch for landing
Committed r286113 (244500@main): <https://commits.webkit.org/244500@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 444972 [details].
<rdar://problem/85679362>