Implement `scroll_view` widget #63

Job	Run time
cargo doc (windows-latest)	2m 34s
cargo fmt	17s
cargo clippy + test (windows-latest)	3m 17s
cargo doc (macos-latest)	2m 21s
cargo clippy + test (macos-latest)	1m 58s
cargo doc (ubuntu-latest)	1m 50s
cargo clippy + test (ubuntu-latest)	1m 30s
	13m 47s

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