*/myth*: update the mythtv family of ports to 33.1

Selected upstream changes:

• The minimum Qt version has been bumped from 5.9 to 5.12
• FFmpeg upgraded to version 5.1
• New Waveform visualisation for MythMusic
• DiSEqC support for SAT>IP
• Automatic channel groups per video source
• Nearly 300 continued code modernization and restructuring (not in commits below)
• Version 2 of the Services API is under development

Changelog: https://www.mythtv.org/wiki/Release_Notes_-_33

PR: 270344