In Reaper, controls tab and info panel not filled initially

[jpcima]

Reproducing the issue

• open Reaper
• load sfizz on master bus
• controls tab does not contain any knobs
• press Play button
• control tab fills up

It's because this info is provided by OSC messages, and messaging works only when the sfizz synth is running.
This info should be cached on load, so that it can be sent regardless whether sfizz is active or not.

[jpcima]

We face a little obstacle at the moment, and there's various possibilities about it.

I wish plugins/common to have a utility that extracts the static info about a loaded instrument all at once.
That's the CC slots, key ranges, switch ranges, and so on.

The LV2 and VST are made with C and C++ sfizz interface respectively.
Because of this, plugins/common would need C and C++ implementations of the same feature.

1. duplicate implementation or find a way to template-hack it
2. convert LV2 to C++ interface, making us lose it as integration test of the C one
3. have a conversion between sfizz interface handles of C and C++, which preserves ABI and ownership