Add insta-based snapshot tests that cover side-by-side format #3256

Job	Run time
Actionlint	1m 20s
Rustfmt	25s
Test x86_64-unknown-linux-gnu	3m 31s
Check Linux Packaging	2m 20s
Test x86_64-apple-darwin	4m 29s
Test Linux (latest stable Rust)	1m 25s
Output Regression Test	3m 31s
Test x86_64-pc-windows-msvc	4m 10s
Test aarch64-unknown-linux-gnu	6m 35s
Test with MIME database	3m 0s
Test aarch64-apple-darwin	3m 7s
Test x86_64-unknown-linux-musl	3m 39s
	37m 32s

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