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

src/plugin/bridges/vst3.cpp

@@ -265,6 +265,28 @@ Vst3PluginBridge::Vst3PluginBridge()
                     return plug_view->plug_frame->resizeView(plug_view,
                                                              &request.new_size);
                 },
+                [&](const YaPlugInterfaceSupport::IsPlugInterfaceSupported&
+                        request) -> YaPlugInterfaceSupport::
+                                     IsPlugInterfaceSupported::Response {
+                                         // TODO: For correctness' sake we
+                                         //       should automatically reject
+                                         //       queries for interfaces we
+                                         //       don't yet or can't implement,
+                                         //       like the ARA interfaces.
+                                         if (request.owner_instance_id) {
+                                             return plugin_proxies
+                                                 .at(*request.owner_instance_id)
+                                                 .get()
+                                                 .plug_interface_support
+                                                 ->isPlugInterfaceSupported(
+                                                     request.iid.data());
+                                         } else {
+                                             return plugin_factory
+                                                 ->plug_interface_support
+                                                 ->isPlugInterfaceSupported(
+                                                     request.iid.data());
+                                         }
+                                     },
                 [&](const YaUnitHandler::NotifyUnitSelection& request)
                     -> YaUnitHandler::NotifyUnitSelection::Response {
                     return plugin_proxies.at(request.owner_instance_id)