Gui: Fix window restoration after Edit->Alignment completion

After completing Edit->Alignment, main window remains small instead of
maximized. It looks like this is Qt 6 regression as the automatic
maximization behavior was somehow changed. Previously it didn't need
explicit handling to restore the maximisation.

So, this patch preserves the previous window state before entering
Alignment editor and restores window being maximized/minimized or normal
upon finishing the operation.

src/Gui/ManualAlignment.cpp

@@ -27,6 +27,7 @@
 # include <QLabel>
 # include <QMenu>
 # include <QMessageBox>
+# include <QMdiSubWindow>
 # include <QPainter>
 # include <QSplitter>
 # include <QSurfaceFormat>
@@ -791,6 +792,18 @@ void ManualAlignment::startAlignment(Base::Type mousemodel)
     if (myAlignModel.isEmpty())
         return;
 
+#if QT_VERSION >= QT_VERSION_CHECK(6,0,0)
+    // save the current window state before opening the alignment viewer
+    previousWindowState = Qt::WindowNoState;
+    if (auto* activeDoc = Gui::Application::Instance->activeDocument()) {
+        if (auto* activeView = activeDoc->getActiveView()) {
+            if (auto* subWindow = qobject_cast<QMdiSubWindow*>(activeView->parentWidget())) {
+                previousWindowState = subWindow->windowState();
+            }
+        }
+    }
+#endif
+
     // create a split window for picking the points
     myViewer = new AlignmentView(myDocument,Gui::getMainWindow());
     myViewer->setWindowTitle(tr("Alignment[*]"));
@@ -874,6 +887,34 @@ void ManualAlignment::closeViewer()
     if (myViewer->parentWidget())
         myViewer->parentWidget()->deleteLater();
     myViewer = nullptr;
+
+#if QT_VERSION >= QT_VERSION_CHECK(6,0,0)
+    QTimer::singleShot(0, [this]() {
+        auto* activeDoc = Gui::Application::Instance->activeDocument();
+        if (!activeDoc) {
+            return;
+        }
+
+        auto* activeView = activeDoc->getActiveView();
+        if (!activeView) {
+            return;
+        }
+
+        Gui::getMainWindow()->setActiveWindow(activeView);
+        if (auto* subWindow = qobject_cast<QMdiSubWindow*>(activeView->parentWidget())) {
+            // restore the previous window state
+            if (previousWindowState & Qt::WindowMaximized) {
+                subWindow->showMaximized();
+            }
+            else if (previousWindowState & Qt::WindowMinimized) {
+                subWindow->showMinimized();
+            }
+            else {
+                subWindow->showNormal();
+            }
+        }
+    });
+#endif
 }
 
 /**

src/Gui/ManualAlignment.h

@@ -262,6 +262,10 @@ private:
     int myPickPoints;
     Base::Placement myTransform;
 
+#if QT_VERSION >= QT_VERSION_CHECK(6,0,0)
+    Qt::WindowStates previousWindowState;
+#endif
+
     class Private;
     Private* d;
 };