Support auxiliary inputs and outputs for CLAP

This does not yet work for VST3. You'll always get empty slices there.

plugins/examples/sine/src/lib.rs

@@ -138,7 +138,12 @@ impl Plugin for Sine {
         self.midi_note_gain.reset(0.0);
     }
 
-    fn process(&mut self, buffer: &mut Buffer, context: &mut impl ProcessContext) -> ProcessStatus {
+    fn process(
+        &mut self,
+        buffer: &mut Buffer,
+        _aux: &mut AuxiliaryBuffers,
+        context: &mut impl ProcessContext,
+    ) -> ProcessStatus {
         let mut next_event = context.next_event();
         for (sample_id, channel_samples) in buffer.iter_samples().enumerate() {
             // Smoothing is optionally built into the parameters themselves