Core: Remove #include <QMainWindow> from icore.h

Adapt users; also use dialogParent() instead of mainWindow() were
appropriate.

Change-Id: Ib60b118f05c986a70657446c5b2937074243bb5c
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

src/plugins/cmakeprojectmanager/cmakebuildsystem.cpp

@@ -412,14 +412,14 @@ bool CMakeBuildSystem::mustApplyConfigurationChangesArguments(const BuildDirPara
     if (parameters.configurationChangesArguments.isEmpty())
         return false;
 
-    auto answer = QMessageBox::question(Core::ICore::mainWindow(),
-                                        tr("Apply configuration changes?"),
-                                        "<p>" + tr("Run CMake with configuration changes?")
-                                            + "</p><pre>"
-                                            + parameters.configurationChangesArguments.join("\n")
-                                            + "</pre>",
-                                        QMessageBox::Apply | QMessageBox::Discard,
-                                        QMessageBox::Apply);
+    int answer = QMessageBox::question(Core::ICore::dialogParent(),
+                                       tr("Apply configuration changes?"),
+                                       "<p>" + tr("Run CMake with configuration changes?")
+                                       + "</p><pre>"
+                                       + parameters.configurationChangesArguments.join("\n")
+                                       + "</pre>",
+                                       QMessageBox::Apply | QMessageBox::Discard,
+                                       QMessageBox::Apply);
     return answer == QMessageBox::Apply;
 }