Conditionally enable bindings for `wasm32-wasi` with `--wasi` flag #1515

Job	Run time
build_benchmarks	1m 22s
build_examples	4m 33s
build_nightly	2m 15s
Check	1m 52s
Verify that web-sys is compiled correctly	1m 15s
Clippy	8m 10s
dist_linux_aarch64_gnu	4m 52s
dist_linux_x86_64_musl	3m 55s
dist_macos_aarch64	3m 23s
dist_macos_x86_64	2m 49s
dist_windows	4m 27s
doc_api	1m 31s
doc_book	20s
Rustfmt	14s
Build and test the deno example	1m 28s
Run js-sys crate tests	3m 18s
Run native tests	2m 47s
Run wasm-bindgen crate tests with multithreading enabled	4m 26s
Test TypeScript output of wasm-bindgen	1m 38s
Run UI compile-fail tests	7m 7s
Run wasm-bindgen crate tests (unix)	9m 12s
Run web-sys crate tests	8m 26s
Run wasm-bindgen-webidl crate tests	3m 48s
test_examples	3m 43s
deploy	1m 8s
	1h 27m 59s

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