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.cpp

@@ -0,0 +1,51 @@
+// 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/>.
+
+#include "host-context-proxy.h"
+
+#include <iostream>
+
+Vst3HostContextProxyImpl::Vst3HostContextProxyImpl(
+    Vst3Bridge& bridge,
+    Vst3HostContextProxy::ConstructArgs&& args)
+    : Vst3HostContextProxy(std::move(args)), bridge(bridge) {
+    // The lifecycle is thos object is managed together with that of the plugin
+    // object instance instance this belongs to
+}
+
+tresult PLUGIN_API
+Vst3HostContextProxyImpl::queryInterface(const Steinberg::TUID _iid,
+                                         void** obj) {
+    // I don't think it's expected of a host to implement multiple interfaces on
+    // this object, so if we do get a call here it's important that it's logged
+    // TODO: Successful queries should also be logged
+    const tresult result = Vst3HostContextProxy::queryInterface(_iid, obj);
+    if (result != Steinberg::kResultOk) {
+        std::cerr << "TODO: Implement unknown interface logging on Wine side"
+                  << std::endl;
+    }
+
+    return result;
+}
+
+tresult PLUGIN_API
+Vst3HostContextProxyImpl::createInstance(Steinberg::TUID cid,
+                                         Steinberg::TUID _iid,
+                                         void** obj) {
+    // TODO: Implement
+    std::cerr << "TODO: IHostApplication::createInstance()" << std::endl;
+    return Steinberg::kNotImplemented;
+}