I was not aware that one could `#if` inside IDL until I stumbled upon another file that did 😅
Created attachment 434112 [details] Patch
Created attachment 434133 [details] Patch
Created attachment 434142 [details] Patch
Created attachment 434146 [details] Patch
Committed r280284 (239942@main): <https://commits.webkit.org/239942@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 434146 [details].
<rdar://problem/81051431>