visionOS: Fix the build for all BaseExtension-derived targets
<rdar://problem/116261778>
Pull request: https://github.com/WebKit/WebKit/pull/18448
Committed 268679@main (de3b4d47e4f7): <https://commits.webkit.org/268679@main> Reviewed commits have been landed. Closing PR #18448 and removing active labels.