Get Bevy building for WebAssembly with multithreading #38311

Job	Run time
build (windows-latest)	5m 23s
build (ubuntu-latest)	2m 13s
build (macos-latest)	7m 24s
ci	1m 36s
miri	5m 56s
run-examples-macos-metal	4m 21s
toml	1m 54s
check-bevy-internal-imports	4s
typos	5s
check-cfg	46s
check-doc	7m 22s
check-missing-examples-in-docs	29s
check-missing-features-in-docs	36s
markdownlint	1m 9s
check-compiles	2m 5s
build-wasm	33s
build-wasm-atomics	18s
msrv	54s
	43m 8s

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