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/projecttree/mesonprojectnodes.cpp

@@ -0,0 +1,83 @@
+/****************************************************************************
+**
+** 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 "mesonprojectnodes.h"
+#include <project/mesonbuildconfiguration.h>
+#include <project/mesonbuildsystem.h>
+#include <mesonpluginconstants.h>
+#include <projectexplorer/project.h>
+#include <projectexplorer/target.h>
+namespace MesonProjectManager {
+namespace Internal {
+
+MesonProjectNode::MesonProjectNode(const Utils::FilePath &directory)
+    : ProjectExplorer::ProjectNode{directory}
+{
+    static const auto MesonIcon = QIcon(Constants::Icons::MESON);
+    setPriority(Node::DefaultProjectPriority + 1000);
+    setIcon(MesonIcon);
+    setListInProject(false);
+}
+
+MesonFileNode::MesonFileNode(const Utils::FilePath &file)
+    : ProjectExplorer::ProjectNode{file}
+{
+    static const auto MesonFolderIcon = Core::FileIconProvider::directoryIcon(
+        Constants::Icons::MESON);
+    setIcon(MesonFolderIcon);
+    setListInProject(true);
+}
+
+MesonTargetNode::MesonTargetNode(const Utils::FilePath &directory, const QString &name)
+    : ProjectExplorer::ProjectNode{directory}
+    , m_name{name}
+{
+    setPriority(Node::DefaultProjectPriority + 900);
+    setIcon(QIcon(":/projectexplorer/images/build.png"));
+    setListInProject(false);
+    setShowWhenEmpty(true);
+    setProductType(ProjectExplorer::ProductType::Other);
+}
+
+void MesonTargetNode::build()
+{
+    ProjectExplorer::Project *p = getProject();
+    ProjectExplorer::Target *t = p ? p->activeTarget() : nullptr;
+    if (t)
+        static_cast<MesonBuildSystem *>(t->buildSystem())->mesonBuildConfiguration()->build(m_name);
+}
+
+QString MesonTargetNode::tooltip() const
+{
+    return {};
+}
+
+QString MesonTargetNode::buildKey() const
+{
+    return m_name;
+}
+
+} // namespace Internal
+} // namespace MesonProjectManager