Improve comment in text layout code #12869

Job	Run time
Check wasm32+atomics	1m 29s
Check wasm32 + wasm-bindgen	2m 17s
cargo-deny aarch64-apple-darwin	40s
android	25s
cargo-deny aarch64-linux-android	40s
Format + check + test	5m 26s
cargo-deny i686-pc-windows-gnu	35s
ios	19s
Check Windows	1m 27s
cargo-deny i686-pc-windows-msvc	42s
cargo-deny i686-unknown-linux-gnu	36s
cargo-deny wasm32-unknown-unknown	36s
cargo-deny x86_64-apple-darwin	40s
cargo-deny x86_64-pc-windows-gnu	35s
cargo-deny x86_64-pc-windows-msvc	35s
cargo-deny x86_64-unknown-linux-gnu	35s
cargo-deny x86_64-unknown-linux-musl	42s
cargo-deny x86_64-unknown-redox	42s
	19m 1s

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