Implements post-process film grain effects #73991

Job	Run time
miri	10m 8s
ci	4m 21s
check-doc	10m 7s
toml	8s
typos	9s
check-release-content	35s
build (ubuntu-latest)	10m 8s
check-bevy-internal-imports	7s
check-missing-examples-in-docs	37s
build (macos-latest)	10m 10s
build (windows-latest)	9m 59s
check-missing-features-in-docs	33s
markdownlint	1m 36s
check-compiles-no-std-examples	0s
check-compiles	0s
check-compiles-no-std-portable-atomic	0s
check-compiles-no-std	0s
build-wasm-atomics	1s
msrv	1s
build-wasm	1s
	58m 41s

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