Reland "Piping audio interruption metrics to API layer"

The metrics are now added as RTCNonStandardStatsMember objects in
RTCMediaStreamTrackStats. Unit tests are updated.

This is a reland of https://webrtc-review.googlesource.com/c/src/+/134303,
with fixes.

TBR=kwiberg@webrtc.org

Bug: webrtc:10549
Change-Id: I29dcc6fbfc69156715664e71acfa054c1b2d9038
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/134500
Commit-Queue: Henrik Lundin <henrik.lundin@webrtc.org>
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Ivo Creusen <ivoc@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27806}
diff --git a/modules/audio_coding/neteq/neteq_impl_unittest.cc b/modules/audio_coding/neteq/neteq_impl_unittest.cc
index 025ed69..8269526 100644
--- a/modules/audio_coding/neteq/neteq_impl_unittest.cc
+++ b/modules/audio_coding/neteq/neteq_impl_unittest.cc
@@ -745,7 +745,7 @@
   }
 
   auto lifetime_stats = neteq_->GetLifetimeStatistics();
-  EXPECT_EQ(0u, lifetime_stats.interruption_count);
+  EXPECT_EQ(0, lifetime_stats.interruption_count);
 }
 
 // This test verifies that NetEq can handle comfort noise and enters/quits codec