ENABLE_PDF_PLUGIN will be true for both macOS and iOS.
<rdar://problem/116557962>
Pull request: https://github.com/WebKit/WebKit/pull/18741
Committed 268999@main (7760f95ca8a6): <https://commits.webkit.org/268999@main> Reviewed commits have been landed. Closing PR #18741 and removing active labels.