Get Bevy building for WebAssembly with multithreading #39241

Job	Run time
miri	5m 49s
ci	3m 19s
check-doc	7m 37s
check-cfg	1m 12s
build (windows-latest)	3m 33s
check-bevy-internal-imports	6s
check-missing-examples-in-docs	30s
build (ubuntu-latest)	1m 53s
run-examples-macos-metal	4m 41s
build (macos-latest)	6m 35s
toml	1m 59s
typos	6s
check-missing-features-in-docs	31s
markdownlint	1m 11s
check-compiles	4m 48s
msrv	1m 24s
build-wasm	1m 23s
build-wasm-atomics	1m 8s
	47m 45s

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