Add `Arc::flipped` #572

Job	Run time
cargo check (msrv) (wasm32)	21s
cargo clippy (wasm32)	37s
cargo clippy (windows-latest)	1m 3s
cargo check (msrv) (windows-latest)	52s
cargo clippy (macos-latest)	42s
cargo doc	23s
cargo check (msrv) (macos-latest)	36s
cargo fmt	22s
cargo clippy (ubuntu-latest)	42s
cargo check (msrv) (ubuntu-latest)	24s
cargo test (windows-latest)	50s
cargo test (wasm32)	21s
cargo test (macos-latest)	25s
typos	5s
cargo test (ubuntu-latest)	22s
	8m 5s

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