Rust

Add `egui_kittest`, a test harness for egui #12987

Job	Run time
android	26s
cargo-deny aarch64-apple-darwin	38s
Check wasm32 + wasm-bindgen	2m 21s
cargo-deny aarch64-linux-android	40s
Check wasm32+atomics	1m 14s
cargo-deny i686-pc-windows-gnu	40s
Format + check + test	3m 13s
cargo-deny i686-pc-windows-msvc	38s
ios	19s
cargo-deny i686-unknown-linux-gnu	38s
cargo-deny wasm32-unknown-unknown	39s
Run tests	1m 10s
cargo-deny x86_64-apple-darwin	39s
Check Windows	1m 43s
cargo-deny x86_64-pc-windows-gnu	37s
cargo-deny x86_64-pc-windows-msvc	38s
cargo-deny x86_64-unknown-linux-gnu	37s
cargo-deny x86_64-unknown-linux-musl	37s
cargo-deny x86_64-unknown-redox	35s
	18m 2s

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