Use handles for queued scenes in SceneSpawner #32454

Job	Run time
build (windows-latest)	3m 10s
check-bevy-internal-imports	4s
check-doc	4m 51s
check-missing-examples-in-docs	30s
build (ubuntu-latest)	1m 47s
build (macos-latest)	3m 55s
ci	1m 43s
miri	5m 40s
run-examples-on-windows-dx12	12m 0s
check-missing-features-in-docs	30s
markdownlint	1m 14s
check-compiles	2m 13s
msrv	55s
build-wasm	44s
	39m 16s

Provide feedback