Prepare to rename RTC_NOTREACHED to RTC_DCHECK_NOTREACHED

Add implementation of RTC_DCHECK_NOTREACHED equal to the RTC_NOTREACHED.
The new macros will replace the old one when old one's usage will be
removed. The idea of the renaming to provide a clear signal that this
is debug build only macros and will be stripped in the production build.

Bug: webrtc:9065
Change-Id: I4c35d8b03e74a4b3fd1ae75dba2f9c05643101db
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/237802
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#35348}
diff --git a/api/video_codecs/video_encoder_config.cc b/api/video_codecs/video_encoder_config.cc
index 0321da2..206a1d3 100644
--- a/api/video_codecs/video_encoder_config.cc
+++ b/api/video_codecs/video_encoder_config.cc
@@ -97,23 +97,24 @@
   } else if (codec->codecType == kVideoCodecVP9) {
     FillVideoCodecVp9(codec->VP9());
   } else {
-    RTC_NOTREACHED() << "Encoder specifics set/used for unknown codec type.";
+    RTC_DCHECK_NOTREACHED()
+        << "Encoder specifics set/used for unknown codec type.";
   }
 }
 
 void VideoEncoderConfig::EncoderSpecificSettings::FillVideoCodecH264(
     VideoCodecH264* h264_settings) const {
-  RTC_NOTREACHED();
+  RTC_DCHECK_NOTREACHED();
 }
 
 void VideoEncoderConfig::EncoderSpecificSettings::FillVideoCodecVp8(
     VideoCodecVP8* vp8_settings) const {
-  RTC_NOTREACHED();
+  RTC_DCHECK_NOTREACHED();
 }
 
 void VideoEncoderConfig::EncoderSpecificSettings::FillVideoCodecVp9(
     VideoCodecVP9* vp9_settings) const {
-  RTC_NOTREACHED();
+  RTC_DCHECK_NOTREACHED();
 }
 
 VideoEncoderConfig::H264EncoderSpecificSettings::H264EncoderSpecificSettings(