GODT-1667: bridge-gui spawns bridge process. [skip-ci]

Other: renaming of bridge-gui.
WIP: locate bridge exe.
WIP: bridge process launch.
WIP: cleaner closure of bridge.
WIP: grpcClient connection retries.
WIP: clean exit when bridge process is killed.

Fixed issues from MR review. [skip-ci].

WIP: Fixed gRPC case in CMakelists.txt [skip-ci]

It caused issues on Debian.

WIP: update gRPC/protobuf and tweaked CMakeLists.txt. [skip-ci]

WIP: Fixed a bug where splash screen could not be dismissed. [skip-ci]

internal/frontend/bridge-gui/EventStreamWorker.h

@@ -0,0 +1,52 @@
+// Copyright (c) 2022 Proton AG
+//
+// This file is part of Proton Mail Bridge.
+//
+// Proton Mail Bridge 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.
+//
+// Proton Mail Bridge 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 Proton Mail Bridge. If not, see <https://www.gnu.org/licenses/>.
+
+
+#ifndef BRIDGE_QT6_EVENT_STREAM_WORKER_H
+#define BRIDGE_QT6_EVENT_STREAM_WORKER_H
+
+
+#include "GRPC/bridge.grpc.pb.h"
+#include "Worker/Worker.h"
+
+
+//****************************************************************************************************************************************************
+/// \brief Stream reader class.
+//****************************************************************************************************************************************************
+class EventStreamReader: public Worker
+{
+    Q_OBJECT
+public: // member functions
+    explicit EventStreamReader(QObject *parent); ///< Default constructor.
+    EventStreamReader(EventStreamReader const&) = delete; ///< Disabled copy-constructor.
+    EventStreamReader(EventStreamReader&&) = delete; ///< Disabled assignment copy-constructor.
+    ~EventStreamReader() override = default; ///< Destructor.
+    EventStreamReader& operator=(EventStreamReader const&) = delete; ///< Disabled assignment operator.
+    EventStreamReader& operator=(EventStreamReader&&) = delete; ///< Disabled move assignment operator.
+
+public slots:
+    void run() override; ///< Run the reader.
+
+signals:
+#pragma clang diagnostic push
+#pragma ide diagnostic ignored "NotImplementedFunctions"
+    void eventReceived(QString eventString); ///< signal for events.
+#pragma clang diagnostic pop
+};
+
+
+#endif //BRIDGE_QT6_EVENT_STREAM_WORKER_H