ClangCodeModel: Switch on clangd's Include Cleaner

Task-number: QTCREATORBUG-147
Task-number: QTCREATORBUG-14040
Change-Id: Ib215ed3bbb6f42d25752c747693371239222e67a
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/clangcodemodel/clangdclient.cpp

@@ -615,6 +615,8 @@ void setupClangdConfigFile()
         saver.write(firstLine + '\n');
         saver.write("Hover:\n");
         saver.write("  ShowAKA: Yes\n");
+        saver.write("Diagnostics:\n");
+        saver.write("  UnusedIncludes: Strict\n");
         QTC_CHECK(saver.finalize());
     }
 }