Add support for `Dictionary` to AST datatype in unparser #39037

Job	Run time
Check License Header	2m 26s
linux build test	4m 58s
build with wasm-pack	3m 28s
cargo test (macos-aarch64)	9m 41s
Check cargo fmt	40s
Verify MSRV (Min Supported Rust Version)	7m 57s
Verify Vendored Code	52s
cargo check no default features	8m 32s
cargo doc	4m 3s
cargo test (amd64)	16m 14s
cargo check datafusion	5m 22s
cargo check functions	2m 15s
cargo test doc (amd64)	17m 31s
cargo examples (amd64)	16m 51s
check Cargo.toml formatting	2m 59s
clippy	5m 50s
check configs.md and ***_functions.md is up-to-date	5m 17s
Run sqllogictest with Postgres runner	5m 53s
cargo test pyarrow (amd64)	4m 21s
verify benchmark results (amd64)	9m 55s
	2h 15m 5s

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