Add `Line::reversed`, `Line::midpoint`, rename `Arc::flipped` #607

Job	Run time
cargo check (msrv) (windows-latest)	55s
cargo clippy (windows-latest)	1m 23s
cargo check (msrv) (wasm32)	25s
cargo check (msrv) (macos-latest)	33s
cargo clippy (wasm32)	38s
cargo clippy (macos-latest)	48s
cargo check (msrv) (ubuntu-latest)	26s
cargo clippy (ubuntu-latest)	47s
cargo doc	22s
cargo fmt	24s
cargo test (windows-latest)	1m 12s
cargo test (wasm32)	21s
cargo test (macos-latest)	24s
typos	5s
cargo test (ubuntu-latest)	18s
	9m 1s

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