Portamento playback for Trombone

There is portamento playback for Muse Strings but not for MuseBrass.

Portamento playback on Trombone (and other MuseBrass and MuseWoodwinds instruments to a lesser extent) would be incredibly useful. Portamento glissando is far more characteristic to trombone than diatonic or chromatic glissando. As playback for portamento glissando has already been implemented for MuseStrings, it would only make sense to do the same for MuseBrass and MuseWoodwinds.