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/settings/tools/toolitemsettings.cpp

@@ -0,0 +1,74 @@
+/****************************************************************************
+**
+** 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 "toolitemsettings.h"
+#include "tooltreeitem.h"
+#include "ui_toolitemsettings.h"
+
+namespace MesonProjectManager {
+namespace Internal {
+ToolItemSettings::ToolItemSettings(QWidget *parent)
+    : QWidget(parent)
+    , ui(new Ui::ToolItemSettings)
+{
+    ui->setupUi(this);
+    ui->mesonPathChooser->setExpectedKind(Utils::PathChooser::ExistingCommand);
+    ui->mesonPathChooser->setHistoryCompleter(QLatin1String("Meson.Command.History"));
+    connect(ui->mesonPathChooser,
+            &Utils::PathChooser::rawPathChanged,
+            this,
+            &ToolItemSettings::store);
+    connect(ui->mesonNameLineEdit, &QLineEdit::textChanged, this, &ToolItemSettings::store);
+}
+
+ToolItemSettings::~ToolItemSettings()
+{
+    delete ui;
+}
+
+void ToolItemSettings::load(ToolTreeItem *item)
+{
+    if (item) {
+        m_currentId = Utils::nullopt;
+        ui->mesonNameLineEdit->setDisabled(item->isAutoDetected());
+        ui->mesonNameLineEdit->setText(item->name());
+        ui->mesonPathChooser->setDisabled(item->isAutoDetected());
+        ui->mesonPathChooser->setFileName(item->executable());
+        m_currentId = item->id();
+    } else {
+        m_currentId = Utils::nullopt;
+    }
+}
+
+void ToolItemSettings::store()
+{
+    if (m_currentId)
+        emit applyChanges(*m_currentId,
+                          ui->mesonNameLineEdit->text(),
+                          ui->mesonPathChooser->fileName());
+}
+
+} // namespace Internal
+} // namespace MesonProjectManager