[ToolTipArea] Add "aboutToShow" signal

This is emitted just before the tooltip is shown and allows the user to defer heavy lifting to when the dialog is actually shown.

Differential Revision: https://phabricator.kde.org/D10381

src/declarativeimports/core/tooltip.cpp

@@ -130,6 +130,8 @@ void ToolTip::showToolTip()
         return;
     }
 
+    emit aboutToShow();
+
     ToolTipDialog *dlg = tooltipDialogInstance();
 
     if (!mainItem()) {

src/declarativeimports/core/tooltip.h

@@ -187,6 +187,12 @@ Q_SIGNALS:
     void locationChanged();
     void activeChanged();
     void interactiveChanged();
+    /**
+     * Emitted just before the tooltip dialog is shown.
+     *
+     * @since 5.45
+     */
+    void aboutToShow();
 
 private Q_SLOTS:
     void settingsChanged(const QString &file);