[WebGPU] Rename the setting from just "WebGPU" to "WebGPUEnabled"
<rdar://problem/109134933>
Pull request: https://github.com/WebKit/WebKit/pull/13680
Committed 264033@main (529569b68016): <https://commits.webkit.org/264033@main> Reviewed commits have been landed. Closing PR #13680 and removing active labels.