Add `Slider::clamping` for precise clamp control #12731

Job	Run time
Format + check + test	5m 55s
android	29s
Check wasm32 + wasm-bindgen	2m 38s
cargo-deny aarch64-apple-darwin	40s
Check wasm32+atomics	1m 20s
ios	31s
cargo-deny aarch64-linux-android	40s
Check Windows	1m 33s
cargo-deny i686-pc-windows-gnu	40s
cargo-deny i686-pc-windows-msvc	36s
cargo-deny i686-unknown-linux-gnu	39s
cargo-deny wasm32-unknown-unknown	36s
cargo-deny x86_64-apple-darwin	37s
cargo-deny x86_64-pc-windows-gnu	42s
cargo-deny x86_64-pc-windows-msvc	40s
cargo-deny x86_64-unknown-linux-gnu	38s
cargo-deny x86_64-unknown-linux-musl	37s
cargo-deny x86_64-unknown-redox	37s
	20m 8s

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