Improvements to glissandi playback

With the improvements MuseScore 4.2 brought to playback for guitar bends, I imagine an improvement for glissando playback could be pretty similar. I think the portamento widget from MuseScore 3 could be adapted to MuseScore 4 is a similar way the Bend editor was.

Additionally, though micro-tonal accidentals do play back when applied to Muse Sounds soundfonts, portamento glissandi currently do not.