Introduce RTC_CHECK_NOTREACHED(), an always-checking RTC_NOTREACHED()

And use it in a few places that were using RTC_CHECK(false) or FATAL()
to do the exact same job. There should be no change in behavior.

Bug: none
Change-Id: I36d5e6bcf35fd41534e08a8c879fa0811b4f1967
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/191963
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32567}

modules/rtp_rtcp/source/create_video_rtp_depacketizer.cc

@@ -37,7 +37,7 @@ std::unique_ptr<VideoRtpDepacketizer> CreateVideoRtpDepacketizer(
     case kVideoCodecMultiplex:
       return std::make_unique<VideoRtpDepacketizerGeneric>();
   }
-  RTC_CHECK(false);
+  RTC_CHECK_NOTREACHED();
 }
 
 }  // namespace webrtc

modules/rtp_rtcp/source/rtp_sender.cc

@@ -128,7 +128,7 @@ bool IsNonVolatile(RTPExtensionType type) {
       RTC_NOTREACHED();
       return false;
   }
-  RTC_CHECK(false);
+  RTC_CHECK_NOTREACHED();
 }
 
 bool HasBweExtension(const RtpHeaderExtensionMap& extensions_map) {

modules/rtp_rtcp/source/rtp_sender_audio.cc

@@ -46,7 +46,7 @@ const char* FrameTypeToString(AudioFrameType frame_type) {
     case AudioFrameType::kAudioFrameCN:
       return "audio_cn";
   }
-  RTC_CHECK(false);
+  RTC_CHECK_NOTREACHED();
 }
 #endif