Rename the VST2 audio processing scratch buffer

Since we also have input and output audio buffers, plain 'buffer' is a
bit too overloaded here.

src/plugin/bridges/vst2.cpp

@@ -617,14 +617,14 @@ void Vst2PluginBridge::do_process(T** inputs, T** outputs, int sample_frames) {
     // After sending these buffers to the Wine plugin host, we'll receive the
     // results back in the same object so we can write back the outputs
     sockets.host_vst_process_replacing.send(process_input_buffers,
-                                            process_buffer);
+                                            process_scratch_buffer);
 
     // NOTE: We use a different object for this, because otherwise
     //       mono-to-stereo plugins or any other configuration where the number
     //       of input channels does not match the number of output channels
     //       would still result in constant reallocations
     sockets.host_vst_process_replacing.receive_single<AudioBuffers>(
-        process_output_buffers, process_buffer);
+        process_output_buffers, process_scratch_buffer);
 
     std::vector<std::vector<T>>& output_audio_buffers =
         std::get<std::vector<std::vector<T>>>(process_output_buffers.buffers);

src/plugin/bridges/vst2.h

@@ -174,7 +174,7 @@ class Vst2PluginBridge : PluginBridge<Vst2Sockets<std::jthread>> {
      * `process()`, `processReplacing()` and `processDoubleReplacing()` calls.
      * This buffer also needs to stay alive.
      */
-    SerializationBuffer<0> process_buffer;
+    SerializationBuffer<0> process_scratch_buffer;
 
     /**
      * We'll periodically synchronize the Wine host's audio thread priority with