Git/DiffEditor: Fix staging added/removed lines separately

Fixes: QTCREATORBUG-23243
Change-Id: Ice19e1c778aabd9cb1b9fe0681234073de85cfcb
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: André Hartmann <aha_1980@gmx.de>
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/diffeditor/diffutils.cpp

@@ -26,6 +26,7 @@
 #include "diffutils.h"
 
 #include <texteditor/fontsettings.h>
+#include <utils/algorithm.h>
 #include <utils/differ.h>
 
 #include <QFutureInterfaceBase>
@@ -37,6 +38,11 @@ using namespace Utils;
 
 namespace DiffEditor {
 
+int ChunkSelection::selectedRowsCount() const
+{
+    return Utils::toSet(leftSelection).unite(Utils::toSet(rightSelection)).count();
+}
+
 static QList<TextLineData> assemblyRows(const QList<TextLineData> &lines,
                                         const QMap<int, int> &lineSpans)
 {