Replaces mix tests based on a strange mix type RDQM{videoId} (only reference I could find is https://github.com/ytdl-org/youtube-dl/issues/26228) and with an invalid video id of 13 characters (the first two characters were QM, but even after removing QM there still wasn't a video available at that id).
Also updates mocks.
* Deprecated Utils#UTF-8; see StandardCharsets
* Added more helpful methods to ``ExtractorAsserts``
* Use parameterized (cool new) tests
* Restore functionality of some tests + updated mockdata
* Other code cleanups + Sonarlint improvements
Stypox
litetex
XiangRongLin
TobiGr