Meson build plugin initial support

Most basic project management is implemented:
- Project config/build
- Build options accessible to user
- Lists most build targets
- Meson and Ninja added to kit setup
- Basic project file tree with files known by Meson
- Some basic meson and ninja process output parsing
- Some project templates

Missing features, that will come later:
- Configurable project tree layout
- Locators for Meson
- Build importer
- Access to Machine files for better user fine tuning
- ...

Fixes: QTCREATORBUG-18117
Change-Id: I2811e71562c113fb0fc6b6177bcf0698fa71ef63
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

src/plugins/mesonprojectmanager/project/mesonprojectimporter.cpp

@@ -0,0 +1,81 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 Alexis Jeandet.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+#include "mesonprojectimporter.h"
+
+#include <QLoggingCategory>
+
+namespace {
+static Q_LOGGING_CATEGORY(mInputLog, "qtc.meson.import", QtWarningMsg);
+}
+
+namespace MesonProjectManager {
+namespace Internal {
+MesonProjectImporter::MesonProjectImporter(const Utils::FilePath &path)
+    : QtSupport::QtProjectImporter{path}
+{}
+
+QStringList MesonProjectImporter::importCandidates()
+{
+    //TODO, this can be done later
+    return {};
+}
+
+QList<void *> MesonProjectImporter::examineDirectory(const Utils::FilePath &importPath) const
+{
+    //TODO, this can be done later
+    qCDebug(mInputLog()) << "examining build directory" << importPath.toUserOutput();
+    QList<void *> data;
+    return data;
+}
+
+bool MesonProjectImporter::matchKit(void *directoryData, const ProjectExplorer::Kit *k) const
+{
+    Q_UNUSED(directoryData)
+    Q_UNUSED(k)
+    //TODO, this can be done later
+    return false;
+}
+
+ProjectExplorer::Kit *MesonProjectImporter::createKit(void *directoryData) const
+{
+    Q_UNUSED(directoryData)
+    //TODO, this can be done later
+    return nullptr;
+}
+
+const QList<ProjectExplorer::BuildInfo> MesonProjectImporter::buildInfoList(void *directoryData) const
+{
+    Q_UNUSED(directoryData)
+    //TODO, this can be done later
+    return {};
+}
+
+void MesonProjectImporter::deleteDirectoryData(void *directoryData) const
+{
+    Q_UNUSED(directoryData)
+}
+
+} // namespace Internal
+} // namespace MesonProjectManager