Add `compute` app function for running compute shaders #765

Job	Run time
nix-fmt-check	26s
nix-flake-check (ubuntu-latest)	25s
cargo (cargo fmt --verbose --all -- --check)	1m 6s
nix-flake-check (macos-latest)	57s
cargo (cargo check --locked --workspace)	58s
cargo (cargo check --locked --examples --workspace)	59s
cargo (cargo test --locked --lib --bins --workspace --features "egui")	1m 7s
cargo (cargo doc --locked --workspace --features "egui")	1m 7s
cargo (cargo test --locked -p nannou_core --no-default-features --features "libm serde")	58s
cargo (mdbook build guide/)	1m 0s
cargo (cargo test --locked -p book_tests)	59s
verifications	0s
guide-push-to-deploy	0s
cargo-publish	0s
	10m 2s

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