Add `UiBuilder::layer_id`, and remove `layer_id` from `Ui::new` #12922

Job	Run time
android	26s
Check wasm32 + wasm-bindgen	2m 32s
Check wasm32+atomics	1m 22s
cargo-deny aarch64-apple-darwin	39s
Format + check + test	2m 47s
cargo-deny aarch64-linux-android	36s
ios	21s
Check Windows	1m 52s
cargo-deny i686-pc-windows-gnu	35s
cargo-deny i686-pc-windows-msvc	34s
cargo-deny i686-unknown-linux-gnu	39s
cargo-deny wasm32-unknown-unknown	38s
cargo-deny x86_64-apple-darwin	39s
cargo-deny x86_64-pc-windows-gnu	37s
cargo-deny x86_64-pc-windows-msvc	37s
cargo-deny x86_64-unknown-linux-gnu	37s
cargo-deny x86_64-unknown-linux-musl	38s
cargo-deny x86_64-unknown-redox	36s
	16m 45s

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