WIP: Allow link_only for posix file sources #30212

Job	Run time
build-client / build-client	9m 44s
setup-selenium / setup_chromedriver	4s
Test (3.8, 0)	41m 22s
Test (3.8, 1)	53m 3s
Test (3.8, 2)	50m 3s
	2h 34m 16s

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