Add enum types for function parameters and return types #1473

Job	Run time
Check	1m 41s
Rustfmt	19s
Clippy	6m 53s
Verify that web-sys is compiled correctly	1m 26s
Run js-sys crate tests	3m 14s
Run native tests	2m 48s
Run wasm-bindgen crate tests with multithreading enabled	4m 2s
Run wasm-bindgen crate tests (unix)	13m 9s
Run web-sys crate tests	7m 29s
Run wasm-bindgen-webidl crate tests	3m 20s
build_benchmarks	1m 24s
build_examples	4m 35s
build_nightly	2m 17s
dist_linux_aarch64_gnu	4m 6s
dist_linux_x86_64_musl	3m 53s
dist_macos_aarch64	2m 5s
dist_macos_x86_64	3m 42s
dist_windows	4m 30s
Build and test the deno example	1m 21s
Test TypeScript output of wasm-bindgen	1m 33s
Run UI compile-fail tests	4m 30s
doc_api	1m 47s
doc_book	25s
test_examples	3m 28s
deploy	1m 12s
	1h 25m 9s

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