OffscreenCanvas.transferToImageBuffer() does not clear WebGL drawing buffer correctly
<rdar://problem/126738038>
Pull request: https://github.com/WebKit/WebKit/pull/27501
Committed 279434@main (c3988b98d7c4): <https://commits.webkit.org/279434@main> Reviewed commits have been landed. Closing PR #27501 and removing active labels.