Add comment explaining DefaultHlsExtractorFactory fallback behaviour

Issue:#8219
PiperOrigin-RevId: 342843964

library/hls/src/main/java/com/google/android/exoplayer2/source/hls/DefaultHlsExtractorFactory.java

@@ -125,6 +125,8 @@ public final class DefaultHlsExtractorFactory implements HlsExtractorFactory {
         return new BundledHlsMediaChunkExtractor(extractor, format, timestampAdjuster);
       }
       if (fileType == FileTypes.TS) {
+        // Fall back on TsExtractor to handle TS streams with an EXT-X-MAP tag. See
+        // https://github.com/google/ExoPlayer/issues/8219.
         fallBackExtractor = extractor;
       }
     }