ClangCodeModel: Fix detection of #ifdef'ed out blocks with clangd

We were erroneously merging adjacent disabled blocks.

Change-Id: I9f8f588c0362d488a24c044910474815b94efd59
Reviewed-by: David Schulz <david.schulz@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>

src/plugins/texteditor/textdocument.h

@@ -172,6 +172,10 @@ signals:
     void fontSettingsChanged();
     void markRemoved(TextMark *mark);
 
+#ifdef WITH_TESTS
+    void ifdefedOutBlocksChanged(const QList<BlockRange> &blocks);
+#endif
+
 protected:
     virtual void applyFontSettings();