refactor(app): Standardize subdomain detection logic #13711

Job	Run time
Setup PHP Version for Code Coverage	4s
Others (8.3) / Sanity Tests	2m 34s
Others (8.4) / Sanity Tests	2m 43s
Others (8.5, --ignore-platform-req=php) / Sanity Tests	3m 1s
Others (8.2) / Sanity Tests	4m 3s
CacheLive	0s
DatabaseLive	-1s
SeparateProcess	-1s
Upload coverage results to Coveralls	-1s
	12m 22s

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