Shrink size of `Shadow` by using `i8/u8` instead of `f32` #13916

Job	Run time
android	21s
cargo-deny aarch64-apple-darwin	51s
cargo-deny aarch64-linux-android	52s
cargo-deny i686-pc-windows-gnu	38s
cargo-deny i686-pc-windows-msvc	40s
Check wasm32 + wasm-bindgen	2m 34s
cargo-deny i686-unknown-linux-gnu	40s
cargo-deny wasm32-unknown-unknown	37s
cargo-deny x86_64-apple-darwin	41s
Check wasm32+atomics	1m 22s
cargo-deny x86_64-pc-windows-gnu	40s
cargo-deny x86_64-pc-windows-msvc	37s
cargo-deny x86_64-unknown-linux-gnu	37s
cargo-deny x86_64-unknown-linux-musl	40s
Format + check + test	2m 27s
cargo-deny x86_64-unknown-redox	37s
ios	23s
Run tests	2m 18s
Check Windows	2m 2s
	19m 37s

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