Only set up VST3 SHM audio buffers in setActive()

This avoids doing the duplicate check (since both `setProcessing()` and
`setActive()` would be called), and this also gets rid of the assumption
added a couple commits ago that `setupProcessing()` is only ever called
once, which is not true.

src/common/serialization/vst3/plugin/audio-processor.h

@@ -178,32 +178,12 @@ class YaAudioProcessor : public Steinberg::Vst::IAudioProcessor {
 
     virtual uint32 PLUGIN_API getLatencySamples() override = 0;
 
-    /**
-     * The response code and written state for a call to
-     * `IAudioProcessor::setupProcessing(setup)`.
-     */
-    struct SetupProcessingResponse {
-        UniversalTResult result;
-        AudioShmBuffer::Config audio_buffers_config;
-
-        template <typename S>
-        void serialize(S& s) {
-            s.object(result);
-            s.object(audio_buffers_config);
-        }
-    };
-
     /**
      * Message to pass through a call to
      * `IAudioProcessor::setupProcessing(setup)` to the Wine plugin host.
-     *
-     * Here Wine plugin host will set up the shared memory buffers.
-     *
-     * NOTE: This process is repeated as part of `SetActive`. Apparently REAPER
-     *       can change bus arrangements after the processing has been set up.
      */
     struct SetupProcessing {
-        using Response = SetupProcessingResponse;
+        using Response = UniversalTResult;
 
         native_size_t instance_id;
 

src/common/serialization/vst3/plugin/component.h

@@ -256,7 +256,7 @@ class YaComponent : public Steinberg::Vst::IComponent {
 
     /**
      * The response code and written state for a call to
-     * `IAudioProcessor::setupProcessing(setup)`.
+     * `IAudioProcessor::setActive(state)`.
      */
     struct SetActiveResponse {
         UniversalTResult result;
@@ -276,7 +276,7 @@ class YaComponent : public Steinberg::Vst::IComponent {
      *
      * NOTE: REAPER may change a plugin's bus arrangements after the processing
      *       has been set up, so we need to check for this on every
-     *       `setActive()` call
+     *       `setActive()` call.
      */
     struct SetActive {
         using Response = SetActiveResponse;

src/common/serialization/vst3/process-data.cpp

@@ -142,7 +142,7 @@ Steinberg::Vst::ProcessData& YaProcessData::reconstruct(
 
     // The actual audio data is contained within a shared memory object, and the
     // input and output pointers point to regions in that object. These pointers
-    // are calculated while handling `IAudioProcessor::setupProcessing()`.
+    // are calculated while handling `IAudioProcessor::setActive()`.
     // NOTE: The 32-bit and 64-bit audio pointers are a union, and since this is
     //       a raw memory buffer we can set either `channelBuffers32` or
     //       `channelBuffers64` to point at that buffer as long as we do the

src/common/serialization/vst3/process-data.h

@@ -83,7 +83,7 @@ class YaProcessData {
      * difficult for us to mess this up, we'll store those bus-channel pointers
      * in `Vst3Bridge::InstanceInterfaces` and we'll point the pointers in our
      * `inputs` and `outputs` fields directly to those pointers. They will have
-     * been set up during `IAudioProcessor::setupProcessing()`.
+     * been set up during `IAudioProcessor::setActive()`.
      *
      * These can be either float or double pointers. Since a pointer is a
      * pointer and they're stored using a union the actual type doesn't matter,