Implement `scroll_view` widget #56

Job	Run time
cargo fmt	14s
cargo clippy + test (windows-latest)	2m 16s
cargo doc (windows-latest)	2m 18s
cargo clippy + test (macos-latest)	1m 52s
cargo doc (macos-latest)	2m 0s
cargo clippy + test (ubuntu-latest)	2m 6s
cargo doc (ubuntu-latest)	1m 36s
	12m 22s

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