Due to sandboxing, in the post-Ventura world it's becoming harder and harder to run WebGL via OpenGL instead of Metal and is not generally useful preference for developers to toggle. Change the status of `WebGLUsingMetal` to `internal` to reflect this.
<rdar://problem/104104772>
Pull request: https://github.com/WebKit/WebKit/pull/8506
Committed 265257@main (4929b4c592f9): <https://commits.webkit.org/265257@main> Reviewed commits have been landed. Closing PR #8506 and removing active labels.