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/test/frame_generator_interface.cc b/api/test/frame_generator_interface.cc
index 356fe3a..fe7b1e8 100644
--- a/api/test/frame_generator_interface.cc
+++ b/api/test/frame_generator_interface.cc
@@ -26,7 +26,7 @@
     case OutputType::kNV12:
       return "NV12";
     default:
-      RTC_NOTREACHED();
+      RTC_DCHECK_NOTREACHED();
   }
 }