Add `run_system_singleton` #32124

Job	Run time
build (windows-latest)	5m 26s
build (ubuntu-latest)	2m 8s
build (macos-latest)	2m 36s
check-bevy-internal-imports	10s
check-doc	4m 8s
check-missing-examples-in-docs	29s
ci	3m 14s
miri	6m 10s
run-examples-on-windows-dx12	15m 57s
check-missing-features-in-docs	57s
markdownlint	1m 26s
check-compiles	2m 15s
build-wasm	56s
msrv	57s
	46m 49s

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