Get Bevy building for WebAssembly with multithreading #38309

Job	Run time
build (windows-latest)	3m 56s
check-doc	7m 56s
build (ubuntu-latest)	1m 49s
check-missing-examples-in-docs	29s
build (macos-latest)	2m 47s
ci	1m 40s
miri	5m 47s
run-examples-macos-metal	4m 21s
toml	2m 4s
typos	6s
check-bevy-internal-imports	4s
check-cfg	48s
check-missing-features-in-docs	30s
markdownlint	1m 9s
check-compiles	2m 17s
build-wasm	45s
msrv	48s
build-wasm-atomics	17s
	37m 33s

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