Fully implement IPlugInterfaceSupport

With this we support all VST 3.6.12 interfaces.

src/plugin/bridges/vst3-impls/plugin-factory.cpp

@@ -111,6 +111,7 @@ YaPluginFactoryImpl::setHostContext(Steinberg::FUnknown* context) {
         // Automatically converted smart pointers for when the plugin performs a
         // callback later
         host_application = host_context;
+        plug_interface_support = host_context;
 
         return bridge.send_message(YaPluginFactory::SetHostContext{
             .host_context_args = Vst3HostContextProxy::ConstructArgs(

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

@@ -32,6 +32,8 @@ class YaPluginFactoryImpl : public YaPluginFactory {
     // `IPluginFactory3::setHostContext()` has been called
 
     Steinberg::FUnknownPtr<Steinberg::Vst::IHostApplication> host_application;
+    Steinberg::FUnknownPtr<Steinberg::Vst::IPlugInterfaceSupport>
+        plug_interface_support;
 
    private:
     Vst3PluginBridge& bridge;

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

@@ -698,6 +698,7 @@ tresult PLUGIN_API Vst3PluginProxyImpl::initialize(FUnknown* context) {
         // Automatically converted smart pointers for when the plugin performs a
         // callback later
         host_application = host_context;
+        plug_interface_support = host_context;
 
         return bridge.send_message(YaPluginBase::Initialize{
             .instance_id = instance_id(),

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

@@ -338,6 +338,8 @@ class Vst3PluginProxyImpl : public Vst3PluginProxy {
     // `IPluginBase::initialize()` has been called
 
     Steinberg::FUnknownPtr<Steinberg::Vst::IHostApplication> host_application;
+    Steinberg::FUnknownPtr<Steinberg::Vst::IPlugInterfaceSupport>
+        plug_interface_support;
 
     // The following pointers are cast from `component_handler` if
     // `IEditController::setComponentHandler()` has been called