0.4.0 Version bump 🎉 #4903

Job	Run time
format	19s
clippy-check	7m 29s
smithay-check-features	5m 16s
check-minimal	1m 59s
anvil-check-features	2m 34s
check-msrv	1m 18s
Documentation on Github Pages	1m 16s
smallvil-check	49s
smithay-tests	2m 43s
WLCS: Core tests	1m 18s
WLCS: Output tests	2m 21s
WLCS: Pointer input tests	1m 13s
WLCS: Bad Buffer Test	1m 26s
	30m 1s

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