Add Theme Switch Widget #12118

Job	Run time
Format + check + test	5m 31s
Check wasm32 + wasm-bindgen	2m 23s
cargo-deny aarch64-apple-darwin	36s
cargo-deny aarch64-linux-android	40s
android	23s
Check Windows	2m 9s
cargo-deny i686-pc-windows-gnu	41s
cargo-deny i686-pc-windows-msvc	40s
cargo-deny i686-unknown-linux-gnu	39s
cargo-deny wasm32-unknown-unknown	41s
cargo-deny x86_64-apple-darwin	38s
cargo-deny x86_64-pc-windows-gnu	38s
cargo-deny x86_64-pc-windows-msvc	38s
cargo-deny x86_64-unknown-linux-gnu	40s
cargo-deny x86_64-unknown-linux-musl	40s
cargo-deny x86_64-unknown-redox	40s
	18m 17s

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