[WebGPU] Add CPU workaround for non-32bpp textures for copyExternalImageToTexture
<rdar://problem/117501593>
Pull request: https://github.com/WebKit/WebKit/pull/19604
Committed 269961@main (014e5f76bd18): <https://commits.webkit.org/269961@main> Reviewed commits have been landed. Closing PR #19604 and removing active labels.