Improve maintainability of DOCTYPE quirks mode detection in `WP_HTML_Doctype_Info` class #35286

Job	Run time
Determine Matrix	3s
Multisite Default / Test current	14m 3s
Single Site Default / Test current	14m 3s
Single Site Memcached / Test current	13m 42s
Single Site Memcached / Test before	14m 7s
Multisite Default / Test before	14m 28s
Single Site Default / Test before	13m 58s
Multisite Memcached / Test current	13m 53s
Multisite Memcached / Test before	13m 17s
Compare / Single Site Default	10s
Compare / Multisite Default	16s
Compare / Single Site Memcached	10s
Compare / Multisite Memcached	16s
Slack Notifications	0s
Failed workflow tasks	-1s
	1h 52m 25s

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