Add function for disabling direct scanout #3704

Job	Run time
format	12s
smithay-check-features	3m 9s
clippy-check	2m 13s
smallvil-check	51s
smithay-tests	2m 46s
anvil-check-features	2m 9s
check-minimal	1m 12s
check-msrv	4m 48s
Documentation on Github Pages	1m 10s
WLCS: Core tests	1m 12s
WLCS: Output tests	1m 20s
WLCS: Pointer input tests	1m 6s
WLCS: Bad Buffer Test	1m 23s
	23m 31s

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