Improve documentation on `LogicalPlan` TreeNode methods #25582

Job	Run time
cargo check	3m 31s
build with wasm-pack	2m 20s
cargo test (macos)	34m 15s
cargo test (macos-aarch64)	9m 2s
Verify Vendored Code	56s
cargo test (win64)	43m 43s
Check cargo fmt	46s
Verify MSRV (Min Supported Rust Version)	6m 32s
cargo test datafusion-cli (amd64)	3m 37s
check configs.md is up-to-date	2m 41s
clippy	5m 2s
circular dependency check	2m 30s
check Cargo.toml formatting	3m 4s
cargo test hash collisions (amd64)	8m 47s
cargo doc	3m 38s
cargo test doc (amd64)	11m 53s
cargo examples (amd64)	10m 23s
Run sqllogictest with Postgres runner	3m 13s
cargo test (amd64)	8m 51s
cargo test pyarrow (amd64)	2m 27s
verify benchmark results (amd64)	10m 8s
	2h 57m 19s

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