This is because ImageBufferShareableBitmapBackend does not set isOriginAtTopLeftCorner = true for CG platform.
Created attachment 431478 [details] Patch
<rdar://78642742>
Created attachment 431492 [details] Patch
Committed r278918 (238849@main): <https://commits.webkit.org/238849@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 431492 [details].