sctk: Add support for `ext-session-lock` protocol #281

Job	Run time
web	1m 52s
native (ubuntu-latest, stable)	3m 46s
native (ubuntu-latest, beta)	4m 13s
native (windows-latest, stable)	5m 4s
native (windows-latest, beta)	4m 11s
native (macOS-latest, stable)	3m 4s
native (macOS-latest, beta)	5m 5s
	27m 15s

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