Implement several multi-layout extensions for VST3

[Quant1um]

This PR implements:

• Multi-layout support for VST3 backend via configurable-audio-ports and audio-ports-config (whichever is present)
• Bus activation flags via audio-ports-activation
• Better support for null-typed ports with arbitrary number of channels (speakerArrFromPortType)
• audio-ports-config implemented for clap-first-example so it could be validated

A similar feature probably needs to be implemented on the AUv2 side, but I don't have enough experience working with AUv2.

[baconpaul]

OK this is a big change. We may want to drop 0.14 first (planned this week) and then put this on next after that.

I also note that your diff changes const char *foo to const char* foo throughout making a lot of diff noise. Any reason fro that? I'm honestly a bit surprised it passed clang format.

[Quant1um]

@baconpaul The formatting change was not intentional, just fixed it! I think it would be a good idea to add PointerAlignment: Right (or Left) to .clang-format, currently pointer alignment seems to be all over the place.

[defiantnerd]

Oh, and audio-ports-config is not suitable for this - the only reason for this extension is a list to be presented to the user. But the settings do not contain enough information so setup the specific busses when it comes to surround/ambisonic.

[Quant1um]

Okay, I removed audio-ports-config extension support; there are still some unresolved questions:

• VST3's setBusArrangements wants the plugin to report a suggested configuration if the plugin doesn't accept the given config. Current implementation defaults to suggesting the current plugin layout. What would the desired behavior be?
• Should this PR also implement 'surround' extension and report layouts with more than 2 channels as CLAP_PORT_SURROUND, or should this be left to a future PR? (currently it reports them as null-typed ports)

[defiantnerd]

I would think ghat suggested config is the current default config - which can be determined from audio-ports. Maybe I am thinking too simple.

[defiantnerd]

Thanks! Very good contribution!