Flush the bus info cache in more places

The current approach 'works', but better err on the safe side. Once this
caching layer is no longer necessary we should just remove it.

src/plugin/bridges/vst3-impls/plugin-proxy.h

@@ -54,6 +54,25 @@ class Vst3PluginProxyImpl : public Vst3PluginProxy {
      */
     bool unregister_context_menu(size_t context_menu_id);
 
+    /**
+     * Clear the bus count and information cache. We need this cache for REAPER
+     * as it makes `num_inputs + num_outputs + 2` function calls to retrieve
+     * this information every single processing cycle. For plugins with a lot of
+     * outputs this really adds up. According to the VST3 workflow diagrams bus
+     * information cannot change anymore once `IAudioProcessor::setProcessing()`
+     * has been called, but REAPER doesn't quite follow the spec here and it
+     * will set bus arrangements and activate the plugin only after it's called
+     * `IAudioProcessor::setProcessing()`. Because of that we'll have to
+     * manually flush this cache when the stores information potentially becomes
+     * invalid.
+     *
+     * HACK: Once REAPER stops calling these functions, we should remove this
+     *       caching layer ASAP as it can only cause issues
+     *
+     * @see processing_bus_cache
+     */
+    void clear_bus_cache();
+
     // From `IAudioPresentationLatency`
     tresult PLUGIN_API
     setAudioPresentationLatencySamples(Steinberg::Vst::BusDirection dir,