feat: Add implicit casting to `TypeSignature::String` #35453

Job	Run time
Check License Header	2m 21s
cargo check	8m 16s
build with wasm-pack	2m 43s
cargo test (macos)	13m 32s
cargo test (macos-aarch64)	17m 30s
Verify Vendored Code	55s
cargo test (win64)	1h 12m 8s
Check cargo fmt	39s
Verify MSRV (Min Supported Rust Version)	8m 47s
cargo test (amd64)	12m 2s
cargo doc	4m 29s
cargo test datafusion-cli (amd64)	4m 22s
cargo examples (amd64)	14m 24s
Run sqllogictest with Postgres runner	4m 11s
verify benchmark results (amd64)	12m 53s
cargo test pyarrow (amd64)	3m 8s
check Cargo.toml formatting	2m 57s
clippy	6m 27s
check configs.md and ***_functions.md is up-to-date	3m 10s
cargo test hash collisions (amd64)	28m 34s
cargo test doc (amd64)	17m 32s
	4h 1m 0s

Provide feedback