[extractors] Use new framework for existing embeds (#4307)

`Brightcove` is difficult to migrate because it's subclasses may depend
on the signature of the current functions. So it is left as-is for now

Note: Tests have not been migrated

yt_dlp/extractor/huffpost.py

@@ -17,6 +17,7 @@ class HuffPostIE(InfoExtractor):
             HPLEmbedPlayer/\?segmentId=
         )
         (?P<id>[0-9a-f]+)'''
+    _EMBED_REGEX = [r'<iframe[^>]+?src=(["\'])(?P<url>https?://embed\.live\.huffingtonpost\.com/.+?)\1']
 
     _TEST = {
         'url': 'http://live.huffingtonpost.com/r/segment/legalese-it/52dd3e4b02a7602131000677',