Support building multiple plugins

[atsushieno]

Currently there are couple of plugins that builds multiple plugin artifacts (and that I am aware of):

• ChowPhaser (Mono/Stereo)
• ADLplug-AE (ADL/OPN)
• DDSP-VST (Effect/Synth)

So far aap-juce build system only brings in one plugin, but that is not ideal. We should be able to build and package multiple plugins within an apk.

[atsushieno]

This turned out to be impossible with current JUCE API by design:

The attached patch is for aap-juce-adlplug-ae (as of eeadd42) that packages both ADLplug and OPNplug within an apk. It packages both native libraries correctly, but only the plugin that was loaded later by System.loadLibrary() at com/rmsl/juce/Java.kt is working. The other results in runtime crashes. It is due to how Android JNI resolves the loaded native symbols and basically there is no remedy unless JUCE itself fixes these possible duplicate symbols issue.

two-plugins.patch

[atsushieno]

Actually it's not 100% JUCE faulty; aap-juce also generates identical function (GetJuceAAPFactory()).