Minor: Move `Monotonicity` to `expr` crate #19201

Job	Run time
cargo check	3m 51s
build with wasm-pack	2m 32s
Check cargo fmt	49s
Verify MSRV	10m 5s
cargo test (mac)	17m 29s
Verify Vendored Code	1m 22s
cargo test (win64)	23m 9s
cargo test (amd64)	15m 49s
cargo test datafusion-cli (amd64)	6m 27s
check Cargo.toml formatting	2m 5s
clippy	8m 5s
check configs.md is up-to-date	3m 21s
cargo test hash collisions (amd64)	16m 40s
cargo doc	5m 14s
cargo test doc (amd64)	17m 7s
cargo examples (amd64)	10m 50s
Run sqllogictest with Postgres runner	5m 49s
cargo test pyarrow (amd64)	3m 23s
verify benchmark results (amd64)	16m 45s
	2h 50m 52s

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