Add `Modal` and `Memory::set_modal_layer` #13296

Job	Run time
android	23s
cargo-deny aarch64-apple-darwin	40s
Check wasm32+atomics	1m 23s
Check wasm32 + wasm-bindgen	2m 26s
Format + check + test	3m 1s
cargo-deny aarch64-linux-android	42s
cargo-deny i686-pc-windows-gnu	41s
ios	25s
cargo-deny i686-pc-windows-msvc	36s
Run tests	1m 49s
cargo-deny i686-unknown-linux-gnu	39s
Check Windows	2m 3s
cargo-deny wasm32-unknown-unknown	39s
cargo-deny x86_64-apple-darwin	39s
cargo-deny x86_64-pc-windows-gnu	40s
cargo-deny x86_64-pc-windows-msvc	39s
cargo-deny x86_64-unknown-linux-gnu	37s
cargo-deny x86_64-unknown-linux-musl	42s
cargo-deny x86_64-unknown-redox	39s
	19m 23s

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