Do not pass Utils::LinkHandler by rvalue ref

There is nothing special about this type that justifies it sticking out
everywhere it appears.

Change-Id: Iccdc95163d477db8a031d0d520f28fea26432a44
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: hjk <hjk@qt.io>

src/plugins/texteditor/texteditor.cpp

@@ -6081,7 +6081,7 @@ void TextEditorWidget::zoomReset()
 }
 
 void TextEditorWidget::findLinkAt(const QTextCursor &cursor,
-                                  Utils::LinkHandler &&callback,
+                                  const Utils::LinkHandler &callback,
                                   bool resolveTarget,
                                   bool inNextSplit)
 {