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/modules/audio_coding/acm2/call_statistics.cc b/modules/audio_coding/acm2/call_statistics.cc
index 0aad594..9f3bdad 100644
--- a/modules/audio_coding/acm2/call_statistics.cc
+++ b/modules/audio_coding/acm2/call_statistics.cc
@@ -45,7 +45,7 @@
     }
     case AudioFrame::kUndefined: {
       // If the audio is decoded by NetEq, `kUndefined` is not an option.
-      RTC_NOTREACHED();
+      RTC_DCHECK_NOTREACHED();
     }
   }
 }