gpu: Implement background polling on Wasm like on non-Wasm. #344

Job	Run time
no_std	33s
build (ubuntu, stable, locked, true)	14m 51s
miri	1m 19s
build (windows, stable, locked, false)	30m 12s
build (macos, stable, locked, false)	18m 30s
build (ubuntu, nightly, locked, false)	15m 4s
build (ubuntu, beta, locked, false)	13m 22s
build (ubuntu, stable, latest, false)	15m 46s
build (ubuntu, stable, minimal, false)	1m 15s
fuzz	14m 23s
features	24m 15s
deploy	7s
	2h 29m 37s

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