Rust

Add `Context::request_discard` for multi-pass layouts #12637

Job	Run time
android	20s
Check wasm32 + wasm-bindgen	46s
cargo-deny aarch64-apple-darwin	41s
cargo-deny aarch64-linux-android	37s
Format + check + test	45s
ios	26s
cargo-deny i686-pc-windows-gnu	38s
cargo-deny i686-pc-windows-msvc	43s
Check Windows	1m 50s
cargo-deny i686-unknown-linux-gnu	42s
cargo-deny wasm32-unknown-unknown	41s
cargo-deny x86_64-apple-darwin	38s
cargo-deny x86_64-pc-windows-gnu	51s
cargo-deny x86_64-pc-windows-msvc	41s
cargo-deny x86_64-unknown-linux-gnu	41s
cargo-deny x86_64-unknown-linux-musl	40s
cargo-deny x86_64-unknown-redox	40s
	12m 20s

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