Fixes #3929 Allow exporting functions named "default". #1978

Job	Run time
Check	57s
build_nightly	1m 37s
build_benchmarks	51s
build_examples	4m 3s
Verify that web-sys is compiled correctly	42s
Clippy	6m 29s
dist_linux_aarch64_gnu	2m 52s
dist_linux_x86_64_musl	10m 34s
dist_macos_aarch64	1m 52s
dist_macos_x86_64	1m 56s
dist_windows	3m 4s
doc_api	1m 6s
doc_book	4s
Rustfmt	8s
Build and test the deno example	45s
Run js-sys crate tests	2m 3s
Run native tests	1m 42s
Run wasm-bindgen crate tests with multithreading enabled	1m 28s
Test TypeScript output of wasm-bindgen	1m 25s
Run UI compile-fail tests	43s
Run wasm-bindgen crate tests (unix)	6m 35s
Run web-sys crate tests	7m 29s
Run wasm-bindgen-webidl crate tests	2m 1s
test_examples	1m 51s
deploy	28s
	1h 2m 45s

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