[extractor/common] Improve m3u8 extraction (closes #12211)

* Extract m3u8 parsing to separate method
* Improve rendition groups extraction
* Build stream name according stream GROUP-ID
* Ignore reference to AUDIO group without URI when stream has no CODECS
+ Add test coverage for parsing m3u8 from #11507, #11995, #12211 and twitch vod

.gitignore

@@ -36,7 +36,6 @@ updates_key.pem
 *.swf
 *.part
 *.swp
-test/testdata
 test/local_parameters.json
 .tox
 youtube-dl.zsh