`ScrollArea` improvements for user configurability #13503

Job	Run time
android	24s
Check wasm32 + wasm-bindgen	40s
cargo-deny aarch64-apple-darwin	39s
cargo-deny aarch64-linux-android	38s
Check wasm32+atomics	1m 22s
cargo-deny i686-pc-windows-gnu	38s
Format + check + test	33s
ios	24s
cargo-deny i686-pc-windows-msvc	39s
Run tests	47s
cargo-deny i686-unknown-linux-gnu	39s
Check Windows	1m 21s
cargo-deny wasm32-unknown-unknown	44s
cargo-deny x86_64-apple-darwin	41s
cargo-deny x86_64-pc-windows-gnu	40s
cargo-deny x86_64-pc-windows-msvc	38s
cargo-deny x86_64-unknown-linux-gnu	41s
cargo-deny x86_64-unknown-linux-musl	39s
cargo-deny x86_64-unknown-redox	37s
	13m 24s

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