Monophonic mode on instrument plugins; portamento

[Monospace-V]

Enhancement Summary

Add a monophonic mode to all native instrument plugins, (and possibly the VST/SF2 plugins too?)
Followed up, possibly, by a portamento option. (Possibly a knob too, that would be cool, for portamento amount.)

Justification

Monophonic mode would be useful.
About portamento: As of now, only the LB302 has a portamento option because the synthesizer originally was monophonic and had portamento.
However, a lot of the time we want a portamento sound with the native plugins, and pitch bending every note to this end is hard. (Perhaps it would be better to be able to pitch bend all native instruments before adding a portamento... I'm not so sure of this, though.)
I don't want to have to use ZASFX or an external VST each time I want one-click portamento.

As an afterthought I'd like to mention I've seen the Kicker being used in ways that can produce long notes (see Jousboxx, Buzzer Beater), and guitars can have glide, though very short- (I'm looking at Vibed). So I generalize all instruments, despite how it might be sensible to exclude ones with a percussive envelope.

[yohannd1]

I'd love to have this.
By the way, for plugins that can't support portamento (I think FluidSynth has that issue, but I can't confirm it), I'm thinking - maybe simulate the portamento with pitch bends? It definitely isn't the same thing, specially with samples (because sample mappings) and synths that have release envelopes, but I think it's a better-than-nothing alternative. Adding an option for this (even if with a warning) would be really nice, because I already do this with pitch bends anyway (it's just more cumbersome)

[zonkmachine]

It looks to me like it would need some similar changes action as #6941
Not the portamento part but the action of quickly 'replacing one note with another'.