str_util: support case‐insensitive string patterns #12451

Job	Run time
Build jj-lib without Git support	45s
build (ubuntu-latest)	4m 11s
build (macos-14)	3m 11s
cargo-deny (advisories)	25s
Check protos	35s
build (windows-latest)	7m 50s
Clippy check	2m 24s
cargo-deny (bans licenses sources)	26s
build (ubuntu-latest, --all-features)	5m 13s
Check that MkDocs can build the docs	22s
Check that MkDocs can build the docs with Poetry 1.8	22s
Check formatting	13s
	25m 57s

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