Rename discarded_primary_packets to packets_discarded.

This it what it is called in the spec:
https://w3c.github.io/webrtc-stats/#dom-rtcreceivedrtpstreamstats-packetsdiscarded

Also log the metric in neteq_rtpplay.

Bug: webrtc:8199
Change-Id: Ie0262d17b913eb6949daa703844d90327eee0aa4
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/263725
Reviewed-by: Minyue Li <minyue@webrtc.org>
Commit-Queue: Jakob Ivarsson‎ <jakobi@webrtc.org>
Reviewed-by: Jakob Ivarsson‎ <jakobi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#37063}

modules/audio_coding/neteq/tools/neteq_stats_plotter.cc

@@ -100,6 +100,8 @@ void NetEqStatsPlotter::SimulationEnded(int64_t simulation_time_ms) {
            lifetime_stats.inserted_samples_for_deceleration);
     printf("  generated_noise_samples: %" PRIu64 "\n",
            lifetime_stats.generated_noise_samples);
+    printf("  packets_discarded: %" PRIu64 "\n",
+           lifetime_stats.packets_discarded);
   }
 }