Make vec2b `Default` #7992

Job	Run time
android	32s
Check wasm32 + wasm-bindgen	3m 11s
Format + check + test	5m 11s
cargo-deny aarch64-apple-darwin	45s
cargo-deny aarch64-linux-android	41s
Check Windows	1m 50s
cargo-deny i686-pc-windows-gnu	41s
cargo-deny i686-pc-windows-msvc	40s
cargo-deny i686-unknown-linux-gnu	40s
cargo-deny wasm32-unknown-unknown	48s
cargo-deny x86_64-apple-darwin	40s
cargo-deny x86_64-pc-windows-gnu	57s
cargo-deny x86_64-pc-windows-msvc	45s
cargo-deny x86_64-unknown-linux-gnu	40s
cargo-deny x86_64-unknown-linux-musl	40s
cargo-deny x86_64-unknown-redox	44s
	19m 25s

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