Support unicode character for `initcap` function #36230

Job	Run time
Check cargo fmt	39s
Check License Header	2m 11s
cargo check	13m 34s
build with wasm-pack	3m 28s
cargo test (macos)	12m 33s
cargo test (macos-aarch64)	11m 51s
Verify MSRV (Min Supported Rust Version)	9m 15s
Verify Vendored Code	48s
cargo test datafusion-cli (amd64)	4m 46s
cargo examples (amd64)	14m 38s
clippy	6m 57s
cargo test hash collisions (amd64)	29m 30s
cargo doc	4m 33s
cargo test (amd64)	12m 30s
cargo test doc (amd64)	18m 9s
Run sqllogictest with Postgres runner	3m 59s
cargo test pyarrow (amd64)	3m 11s
verify benchmark results (amd64)	14m 59s
check Cargo.toml formatting	2m 54s
check configs.md and ***_functions.md is up-to-date	3m 46s
	2h 54m 11s

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