Rewrite video_loopback to use new mac capturer.

The old one has been deprecated for a long time.

Bug: webrtc:6333, webrtc:6898, webrtc:7861
Change-Id: Ib9b798262817e80019afcacc5b41d18957a28101
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/124827
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Reviewed-by: Peter Hanspers <peterhanspers@webrtc.org>
Commit-Queue: Kári Helgason <kthelgason@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26993}

sdk/BUILD.gn

@@ -366,6 +366,7 @@ if (is_ios || is_mac) {
         "..:common_objc",
         ":used_from_extension",
       ]
+      libs = [ "VideoToolbox.framework" ]
     }
 
     rtc_static_library("video_objc") {