MacOS should also forward the caption bitmaps to the UI process, as was done for iOS in 262487@main.
<rdar://problem/107560995>
Pull request: https://github.com/WebKit/WebKit/pull/12323
Committed 262591@main (fc633e7073a2): <https://commits.webkit.org/262591@main> Reviewed commits have been landed. Closing PR #12323 and removing active labels.