visionOS: Enable GPU Process for WebGL (and WebXR, indirectly)
<rdar://problem/114834238>
Pull request: https://github.com/WebKit/WebKit/pull/20218
Committed 270456@main (9594518baf45): <https://commits.webkit.org/270456@main> Reviewed commits have been landed. Closing PR #20218 and removing active labels.