Create Vst3HostContextProxy from YaHostApplication

This is quite a huge refactor, but note everything is consistent (and
we're going to need one or two more of these `Vst3*Proxy` objects).
Right now nothing extends `IHostApplication`, but this way it will be
trivial to add support for more host context interfaces.

src/wine-host/bridges/vst3-impls/host-context-proxy.h

@@ -0,0 +1,40 @@
+// yabridge: a Wine VST bridge
+// Copyright (C) 2020  Robbert van der Helm
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+#pragma once
+
+#include "../vst3.h"
+
+class Vst3HostContextProxyImpl : public Vst3HostContextProxy {
+   public:
+    Vst3HostContextProxyImpl(Vst3Bridge& bridge,
+                             Vst3HostContextProxy::ConstructArgs&& args);
+
+    /**
+     * We'll override the query interface to log queries for interfaces we do
+     * not (yet) support.
+     */
+    tresult PLUGIN_API queryInterface(const Steinberg::TUID _iid,
+                                      void** obj) override;
+
+    // From `IHostApplication`
+    tresult PLUGIN_API createInstance(Steinberg::TUID cid,
+                                      Steinberg::TUID _iid,
+                                      void** obj) override;
+
+   private:
+    Vst3Bridge& bridge;
+};