Add support for enums with negative discriminants #2687

Job	Run time
build_benchmarks	56s
Verify that web-sys is compiled correctly	50s
build_examples	3m 35s
build_nightly	1m 40s
Check	1m 5s
Clippy	2m 53s
Clippy (project)	2m 22s
Clippy (web-sys)	2m 58s
dist_linux_aarch64_gnu	3m 7s
dist_linux_x86_64_musl	2m 31s
dist_macos_aarch64	1m 16s
dist_macos_x86_64	1m 23s
dist_windows	3m 29s
doc_api	1m 10s
doc_book	9s
Check MSRV for CLI tools	34s
Check MSRV for libraries	1s
Rustfmt	6s
Taplo	8s
Run native tests	2m 8s
Build and test the deno example	48s
Run wasm-bindgen crate tests with multithreading	1m 38s
Run UI compile-fail tests	46s
Run wasm-bindgen crate tests (wasm-bindgen)	1m 48s
Run wasm-bindgen crate tests with externref feature	1m 32s
Run wasm-bindgen wasm test	1m 17s
Run wasm-bindgen crate tests (wasm-bindgen (serde-serialize))	1m 49s
Run wasm-bindgen crate tests with multi-value feature	1m 23s
Run wasm-bindgen crate tests (wasm-bindgen (enable-interning))	1m 21s
Run web-sys tests (with geckodriver)	26s
Run web-sys (all features) tests (with geckodriver)	3m 5s
Run web-sys (unstable, all features) tests (with geckodriver)	3m 27s
Run js-sys tests (with geckodriver)	1m 24s
Run js-sys (unstable) tests (with geckodriver)	2m 34s
Run wasm-bindgen-webidl tests (with geckodriver)	32s
Run webidl-tests tests (with geckodriver)	1m 13s
Run webidl-tests (unstable) tests (with geckodriver)	1m 18s
Run typescript-tests tests (with geckodriver)	1m 39s
test_nightly	48s
test_examples	1m 42s
deploy	41s
	1h 3m 32s

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