Add `compute` app function for running compute shaders #750

Job	Run time
nix-flake-check (ubuntu-latest)	23s
nix-fmt-check	22s
nix-flake-check (macos-latest)	54s
cargo (cargo fmt --verbose --all -- --check)	29s
cargo (cargo check --locked --workspace)	37s
cargo (cargo check --locked --examples --workspace)	27s
cargo (cargo test --locked --lib --bins --workspace --features "egui")	29s
cargo (cargo doc --locked --workspace --features "egui")	30s
cargo (cargo test --locked -p nannou_core --no-default-features --features "libm serde")	26s
cargo (mdbook build guide/)	31s
cargo (cargo test --locked -p book_tests)	31s
verifications	0s
guide-push-to-deploy	0s
cargo-publish	0s
	5m 39s

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