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}

modules/audio_coding/codecs/isac/isac_webrtc_api_test.cc

@@ -51,8 +51,8 @@ std::unique_ptr<PCMFile> GetPcmTestFileReader(int sample_rate_hz) {
       filename = test::ResourcePath("audio_coding/testfile32kHz", "pcm");
       break;
     default:
-      RTC_NOTREACHED() << "No test file available for " << sample_rate_hz
-                       << " Hz.";
+      RTC_DCHECK_NOTREACHED()
+          << "No test file available for " << sample_rate_hz << " Hz.";
   }
   auto pcm_file = std::make_unique<PCMFile>();
   pcm_file->ReadStereo(false);

modules/audio_coding/codecs/legacy_encoded_audio_frame_unittest.cc

@@ -88,7 +88,7 @@ class SplitBySamplesTest : public ::testing::TestWithParam<NetEqDecoder> {
         samples_per_ms_ = 8;
         break;
       default:
-        RTC_NOTREACHED();
+        RTC_DCHECK_NOTREACHED();
         break;
     }
   }