Fix build with Qt 6

Amends 14ee4654c1.

Change-Id: I07d4de825fc16727ae71e5fa519074dddf4b4f80
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/texteditor/textdocument.h

@@ -26,6 +26,7 @@
 #pragma once
 
 #include "texteditor_global.h"
+#include "blockrange.h"
 #include "formatter.h"
 #include "indenter.h"
 
@@ -49,7 +50,6 @@ QT_END_NAMESPACE
 
 namespace TextEditor {
 
-class BlockRange;
 class CompletionAssistProvider;
 class ExtraEncodingSettings;
 class FontSettings;