LV2: sfizz fails to instantiate

[atsushieno]

Our LV2 implementation was based on aap-lv2, which successfully instantiates sfizz. Something is inconsistent between this and aap-lv2.

AU and VST3 works fine (I don't see sfizz-multi on AU though).

[atsushieno]

Instancing now works, but attempt to show GUI leads to crash.

[atsushieno]

We have to rewrite Claude's some hacky parts in current writeFunction() implementation that drops "unsupporteed by remidy" parameters even to DSP (where remidy support does not matter). It cannot dispatch file path parameters selected on the UI to the DSP.

[atsushieno]

LV2 sfizz on macOS has been broken and sfizz-ui developers don't care about merging my fixes sfztools/sfizz-ui#154 so I would leave this as is.