Implement `scroll_view` widget #69

Job	Run time
cargo fmt	11s
cargo doc (windows-latest)	56s
cargo clippy + test (windows-latest)	54s
cargo doc (macos-latest)	2m 6s
cargo clippy + test (macos-latest)	51s
cargo doc (ubuntu-latest)	31s
cargo clippy + test (ubuntu-latest)	1m 6s
	6m 35s

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