Standardize copyright headers. #5765

Job	Run time
druid doctests	1m 30s
cargo fmt	21s
mdbook build	15s
Docs (windows-latest)	2m 10s
Docs (macos-latest)	2m 54s
cargo clippy+test (windows-latest)	2m 36s
Docs (ubuntu-latest)	3m 49s
cargo clippy+test (gtk)	3m 15s
cargo clippy+test (macos-latest)	3m 34s
cargo test (wasm32)	2m 38s
cargo clippy+test (ubuntu-latest)	2m 9s
cargo clippy+test (wayland)	1m 55s
	27m 6s

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