cellMusic: implement qt music playback

[Megamouse]

This adds a Qt music handler to the settings dialog.
The music handler currently only exists for cellMusic playback, which is mostly used to play mp3 and other music files.
I chose Qt as a proof of concept.
I don't claim that this is a proper solution, but it is certainly enough to play some custom music and have fun, which is what this is all about anyway.

Btw, this also contains some stuff I implemented for cellMusicDecode. I hope I didn't commit any unused code.

TODO:

• playlists/albums [postponed]
• proper location in Settings dialog / config.yml
• enable by default ?

fixes #10457

[nitroos-ai]

These messages are showing up in terminal in linux but emulator works normally.

(rpcs3:11395): GLib-GObject-CRITICAL **: 20:51:36.729: g_object_set: assertion 'G_IS_OBJECT (object)' failed

(rpcs3:11395): GStreamer-CRITICAL **: 20:51:36.729: gst_object_ref: assertion 'object != NULL' failed

(rpcs3:11395): GStreamer-CRITICAL **: 20:51:36.729: gst_bin_add_many: assertion 'GST_IS_ELEMENT (element_1)' failed

(rpcs3:11395): GStreamer-CRITICAL **: 20:51:36.729: gst_element_link_pads_full: assertion 'GST_IS_ELEMENT (src)' failed

(rpcs3:11395): GStreamer-CRITICAL **: 20:51:36.729: gst_element_get_static_pad: assertion 'GST_IS_ELEMENT (element)' failed

(rpcs3:11395): GStreamer-CRITICAL **: 20:51:36.729: gst_ghost_pad_new: assertion 'GST_IS_PAD (target)' failed

(rpcs3:11395): GStreamer-CRITICAL **: 20:51:36.729: gst_element_add_pad: assertion 'GST_IS_PAD (pad)' failed

(rpcs3:11395): GStreamer-CRITICAL **: 20:51:36.729: gst_object_unref: assertion 'object != NULL' failed