Enable non-literal k in MAP[k], in get_field UDF. #338

Job	Run time
Check cargo fmt	42s
cargo check	3m 30s
build with wasm-pack	2m 26s
cargo test (macos)	6m 7s
cargo test (macos-aarch64)	4m 27s
Verify MSRV (Min Supported Rust Version)	4m 18s
Verify Vendored Code	51s
cargo test (win64)	9m 58s
cargo test (amd64)	6m 42s
cargo test doc (amd64)	12m 38s
cargo test datafusion-cli (amd64)	3m 50s
cargo examples (amd64)	12m 20s
cargo doc	2m 5s
check Cargo.toml formatting	3m 10s
clippy	1m 57s
check configs.md is up-to-date	3m 10s
cargo test hash collisions (amd64)	6m 35s
Run sqllogictest with Postgres runner	3m 22s
cargo test pyarrow (amd64)	2m 52s
verify benchmark results (amd64)	10m 24s
	1h 41m 24s

Provide feedback