Implement getters for WebIDL dictionaries #1984

Job	Run time
Check	56s
build_nightly	1m 36s
build_benchmarks	51s
build_examples	3m 58s
Verify that web-sys is compiled correctly	45s
Clippy	2m 22s
dist_linux_aarch64_gnu	2m 41s
dist_linux_x86_64_musl	2m 22s
dist_macos_aarch64	1m 7s
dist_macos_x86_64	1m 9s
dist_windows	3m 12s
doc_api	1m 9s
doc_book	6s
Rustfmt	9s
Build and test the deno example	48s
Run js-sys crate tests	2m 16s
Run native tests	1m 42s
Run wasm-bindgen crate tests with multithreading enabled	1m 30s
Test TypeScript output of wasm-bindgen	1m 29s
Run UI compile-fail tests	42s
Run wasm-bindgen crate tests (unix)	8m 20s
Run web-sys crate tests	9m 29s
Run wasm-bindgen-webidl crate tests	1m 29s
test_examples	1m 52s
deploy	30s
	52m 30s

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