Make RTCEncodedVideoFrameMetadata.contributingSources undefined if empty
Created attachment 426010 [details] Patch
Created attachment 426085 [details] Patch for landing
Committed r276018 (236570@main): <https://commits.webkit.org/236570@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 426085 [details].
<rdar://problem/76699419>