Implement getters for WebIDL dictionaries #1987

Job	Run time
Check	57s
Clippy	6m 58s
Run native tests	1m 38s
Verify that web-sys is compiled correctly	44s
Run js-sys crate tests	2m 6s
Rustfmt	11s
Run wasm-bindgen crate tests with multithreading enabled	3m 22s
Run wasm-bindgen crate tests (unix)	4m 35s
Run web-sys crate tests	5m 41s
Run wasm-bindgen-webidl crate tests	1m 33s
build_benchmarks	51s
build_examples	3m 57s
build_nightly	1m 35s
dist_linux_aarch64_gnu	2m 39s
dist_linux_x86_64_musl	2m 18s
dist_macos_aarch64	1m 23s
dist_macos_x86_64	1m 11s
doc_book	8s
dist_windows	3m 25s
Build and test the deno example	50s
Test TypeScript output of wasm-bindgen	1m 25s
Run UI compile-fail tests	42s
doc_api	1m 16s
test_examples	1m 52s
deploy	31s
	51m 48s

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