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Fix #15136 (gui: rewrite the online help) #2048

Job	Run time
build (ubsan, -DANALYZE_UNDEFINED=On, true, process, true)	44m 34s
build (tsan, -DANALYZE_THREAD=On, false, thread, false, --executor=thread --error-exitcode=0)	18m 53s
build (asan, -DANALYZE_ADDRESS=On, true, process, false)	22m 21s
	1h 25m 48s