refactor: Fix incomplete SFINAE issues with public slots

Using a class as a slot parameter requires it to be fully
defined. Qt checks that to ensure correct behaviour.

The checking is done via templates, where the SFINAE principle
means that an incomplete class doesn't lead to errors. This
can lead to issues when selecting the appropriate template, hence
GCC warns about that.

In the cases where issues can occur, this commit includes the full
class definition.

Thanks to @letsfindaway for the precise investigation.

Author: Vekhir

src/board/UBBoardController.h

@@ -39,13 +39,18 @@
 
 #include "core/UB.h"
 #include "core/UBApplicationController.h"
+
 #include "document/UBDocumentContainer.h"
 
+#include "domain/UBGraphicsMediaItem.h"
+
+#include "gui/UBBackgroundRuling.h"
+#include "gui/UBToolWidget.h"
+
 class UBMainWindow;
 class UBApplication;
 class UBBoardView;
 
-class UBBackgroundRuling;
 class UBBackgroundManager;
 class UBDocument;
 class UBDocumentController;
@@ -54,11 +59,9 @@ class UBGraphicsScene;
 class UBDocumentProxy;
 class UBEmbedController;
 class UBBlackoutWidget;
-class UBToolWidget;
 class UBVersion;
 class UBSoftwareUpdate;
 class UBSoftwareUpdateDialog;
-class UBGraphicsMediaItem;
 class UBGraphicsWidgetItem;
 class UBBoardPaletteManager;
 class UBItem;

src/domain/UBGraphicsScene.h

@@ -25,28 +25,30 @@
  */
 
 
+
+
 #ifndef UBGRAPHICSSCENE_H_
 #define UBGRAPHICSSCENE_H_
 
 #include <QtGui>
 #include <optional>
 
+#include "core/UB.h"
+
 #include "frameworks/UBCoreGraphicsScene.h"
 
-#include "core/UB.h"
+#include "gui/UBBackgroundRuling.h"
 
+#include "UBGraphicsTextItem.h"
 #include "UBItem.h"
 
-class UBBackgroundRuling;
 class UBGraphicsPixmapItem;
 class UBGraphicsSvgItem;
 class UBGraphicsPolygonItem;
 class UBGraphicsMediaItem;
 class UBGraphicsWidgetItem;
 class UBGraphicsW3CWidgetItem;
-class UBToolWidget;
 class UBGraphicsPDFItem;
-class UBGraphicsTextItem;
 class UBGraphicsRuler;
 class UBGraphicsProtractor;
 class UBGraphicsCompass;

src/podcast/UBPodcastController.h

@@ -36,8 +36,9 @@
 
 #include "core/UBApplicationController.h"
 
+#include "web/simplebrowser/webview.h"
+
 class UBGraphicsScene;
-class WebView;
 class UBPodcastRecordingPalette;
 
 class UBDesktopPortal;

src/web/UBWebController.h

@@ -32,15 +32,15 @@
 
 #include <QtGui>
 #include <QRegularExpression>
-
 #include <QWebEnginePage>
 #include <QWebEngineUrlRequestInterceptor>
 
-#include "UBEmbedContent.h"
 #include "simplebrowser/downloadmanagerwidget.h"
+#include "simplebrowser/webview.h"
+
+#include "UBEmbedContent.h"
 
 class BrowserWindow;
-class WebView;
 class QMenu;
 class QWebEngineProfile;
 class QWebEngineView;

src/web/simplebrowser/browserwindow.h

@@ -56,14 +56,15 @@
 #include <QTime>
 #include <QWebEnginePage>
 
+#include "webview.h"
+
 QT_BEGIN_NAMESPACE
 class QLineEdit;
 class QProgressBar;
 class QStatusBar;
 QT_END_NAMESPACE
 
 class TabWidget;
-class WebView;
 class WBHistoryManager;
 
 class BrowserWindow : public QWidget