Propagate clock through Environment into ObjCVideoTrackSource

In particular ensure it is the same Environment and thus the same clock
as the rest of PeerConnectionFactory uses

Bug: webrtc:42223992
Change-Id: I0a408fc16f803b50b48c9c24f1e8e622776cc8be
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/423420
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#46167}