Mark ghost nodes as experimental and partially feature flag them #51253

Job	Run time
ci	2m 55s
build (windows-latest)	4m 43s
check-doc	8m 45s
build (ubuntu-latest)	2m 48s
check-bevy-internal-imports	4s
build (macos-latest)	2m 5s
check-missing-examples-in-docs	29s
miri	10m 32s
run-examples-macos-metal	5m 55s
toml	1m 54s
typos	11s
check-missing-features-in-docs	35s
markdownlint	1m 11s
check-compiles	4m 55s
check-compiles-no-std	33s
build-wasm-atomics	1m 33s
msrv	57s
build-wasm	47s
	50m 52s

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