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/pc/webrtc_sdp_unittest.cc b/pc/webrtc_sdp_unittest.cc
index a2a884a..883249c 100644
--- a/pc/webrtc_sdp_unittest.cc
+++ b/pc/webrtc_sdp_unittest.cc
@@ -966,7 +966,7 @@
       break;
     case RtpTransceiverDirection::kStopped:
     default:
-      RTC_NOTREACHED();
+      RTC_DCHECK_NOTREACHED();
       new_direction = "a=sendrecv";
       break;
   }
@@ -1602,7 +1602,7 @@
     } else if (mline_index == 1) {
       content_name = kVideoContentName;
     } else {
-      RTC_NOTREACHED();
+      RTC_DCHECK_NOTREACHED();
     }
     TransportInfo transport_info(content_name,
                                  TransportDescription(ufrag, pwd));